* [PATCH 0/3] riscv: Deprecate userspace vector control interfaces
@ 2026-10-07 8:51 Samuel Holland
2026-10-07 8:51 ` [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE Samuel Holland
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Samuel Holland @ 2026-10-07 8:51 UTC (permalink / raw)
To: Paul Walmsley, Anup Patel, Atish Patra
Cc: Palmer Dabbelt, linux-kernel, kvm-riscv, linux-riscv, Andy Chiu,
Samuel Holland
After several discussions within RISE and at Linux Plumbers 2026,
consensus is that these controls create more trouble than benefits, and
should not be used. glibc will not support using them[1], and we don't
know of other users. There is also no plan to add similar controls for
future extensions that add register state (e.g. matrix).
Let's deprecate them now, hiding them behind a default-disabled Kconfig
option so distributions can avoid exposing them. Hopefully they will not
pick up any new users, and we can remove them in the future.
[1]: https://inbox.sourceware.org/libc-alpha/20261006134856.42295-1-palmer@dabbelt.com/
Samuel Holland (3):
riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE
riscv: Deprecate vector state prctl/sysctl
RISC-V: KVM: Decouple vector prctl state from VM ISA
arch/riscv/Kconfig | 13 ++++++-------
arch/riscv/include/asm/processor.h | 4 +++-
arch/riscv/include/asm/vector.h | 16 ++++++++++++----
arch/riscv/kernel/vector.c | 12 +++++++++++-
arch/riscv/kvm/isa.c | 3 ---
5 files changed, 32 insertions(+), 16 deletions(-)
--
2.52.0
base-commit: a90ee4305c4a5df72c11b31dacfdc76e00fcf78a
branch: up/deprecate-prctl
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE
2026-10-07 8:51 [PATCH 0/3] riscv: Deprecate userspace vector control interfaces Samuel Holland
@ 2026-10-07 8:51 ` Samuel Holland
2026-10-13 16:59 ` Andy Chiu
2026-10-07 8:51 ` [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl Samuel Holland
2026-10-07 8:51 ` [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA Samuel Holland
2 siblings, 1 reply; 7+ messages in thread
From: Samuel Holland @ 2026-10-07 8:51 UTC (permalink / raw)
To: Paul Walmsley, Anup Patel, Atish Patra
Cc: Palmer Dabbelt, linux-kernel, kvm-riscv, linux-riscv, Andy Chiu,
Samuel Holland
The ability to prevent userspace from executing vector instructions was
provided as a escape hatch for software that was broken by adding vector
state to the signal context. This appears to be unused in practice, and
creates confusion in the extension support returned by hwprobe(), as in
this one special case an extension reported as present by hwprobe() is
unusable.
Since we believe it is safe to always allow vector usage, start removing
this functionality by dropping the Kconfig option. It is possible to get
equivalent behavior by setting the sysctl at boot via the kernel command
line, but that method will also soon be deprecated.
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---
arch/riscv/Kconfig | 11 -----------
arch/riscv/kernel/vector.c | 2 +-
2 files changed, 1 insertion(+), 12 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index d6c2dbf8455ce..e26450f0d38fb 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -650,17 +650,6 @@ config RISCV_ISA_V
If you don't know what to do here, say Y.
-config RISCV_ISA_V_DEFAULT_ENABLE
- bool "Enable userspace Vector by default"
- depends on RISCV_ISA_V
- default y
- help
- Say Y here if you want to enable Vector in userspace by default.
- Otherwise, userspace has to make explicit prctl() call to enable
- Vector, or enable it via the sysctl interface.
-
- If you don't know what to do here, say Y.
-
config RISCV_ISA_V_UCOPY_THRESHOLD
int "Threshold size for vectorized user copies"
depends on RISCV_ISA_V
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index b112166d51e9f..9641343732782 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -20,7 +20,7 @@
#include <asm/ptrace.h>
#include <asm/bug.h>
-static bool riscv_v_implicit_uacc = IS_ENABLED(CONFIG_RISCV_ISA_V_DEFAULT_ENABLE);
+static bool riscv_v_implicit_uacc = true;
static struct kmem_cache *riscv_v_user_cachep;
#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
static struct kmem_cache *riscv_v_kernel_cachep;
--
2.52.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl
2026-10-07 8:51 [PATCH 0/3] riscv: Deprecate userspace vector control interfaces Samuel Holland
2026-10-07 8:51 ` [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE Samuel Holland
@ 2026-10-07 8:51 ` Samuel Holland
2026-10-13 16:57 ` Andy Chiu
2026-10-07 8:51 ` [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA Samuel Holland
2 siblings, 1 reply; 7+ messages in thread
From: Samuel Holland @ 2026-10-07 8:51 UTC (permalink / raw)
To: Paul Walmsley, Anup Patel, Atish Patra
Cc: Palmer Dabbelt, linux-kernel, kvm-riscv, linux-riscv, Andy Chiu,
Samuel Holland
The ability to prevent userspace from executing vector instructions was
provided as a escape hatch for software that was broken by adding vector
state to the signal context. This appears to be unused in practice, and
creates confusion in the extension support returned by hwprobe(), as in
this one special case an extension reported as present by hwprobe() is
unusable.
Since we believe it is safe to always allow vector usage, hide the prctl
and sysctl behind a Kconfig option and mark them as deprecated, so they
can be removed in the future. Note that significant userspace software
like glibc already considers these controls explicitly unsupported.
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---
arch/riscv/Kconfig | 10 ++++++++++
arch/riscv/include/asm/processor.h | 4 +++-
arch/riscv/include/asm/vector.h | 16 ++++++++++++----
arch/riscv/kernel/vector.c | 10 ++++++++++
4 files changed, 35 insertions(+), 5 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e26450f0d38fb..83e52a0a85ba7 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -650,6 +650,16 @@ config RISCV_ISA_V
If you don't know what to do here, say Y.
+config RISCV_ISA_V_VSTATE_CTRL
+ bool "Deprecated prctl/sysctl for disallowing userspace vector access"
+ depends on RISCV_ISA_V
+ help
+ Add prctl and sysctl interfaces to disallow userspace to execute
+ vector instructions. These controls are deprecated because they create
+ ambiguity in the ISA extension availability reported by hwprobe.
+
+ If you don't know what to do here, say N.
+
config RISCV_ISA_V_UCOPY_THRESHOLD
int "Threshold size for vectorized user copies"
depends on RISCV_ISA_V
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 815715c67f940..ad64df01417a2 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -121,7 +121,9 @@ struct thread_struct {
unsigned long envcfg;
unsigned long sum;
u32 riscv_v_flags;
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
u32 vstate_ctrl;
+#endif
struct __riscv_v_ext_state vstate;
unsigned long align_ctl;
struct __riscv_v_ext_state kernel_vstate;
@@ -202,7 +204,7 @@ extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src
extern unsigned long signal_minsigstksz __ro_after_init;
-#ifdef CONFIG_RISCV_ISA_V
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
/* Userspace interface for PR_RISCV_V_{SET,GET}_VS prctl()s: */
#define RISCV_V_SET_CONTROL(arg) riscv_v_vstate_ctrl_set_current(arg)
#define RISCV_V_GET_CONTROL() riscv_v_vstate_ctrl_get_current()
diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index fffe72a772080..5425a25f8a196 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -404,9 +404,6 @@ static inline void __switch_to_vector(struct task_struct *prev,
}
}
-void riscv_v_vstate_ctrl_init(struct task_struct *tsk);
-bool riscv_v_vstate_ctrl_user_allowed(void);
-
#else /* ! CONFIG_RISCV_ISA_V */
struct pt_regs;
@@ -418,7 +415,6 @@ static __always_inline bool has_xtheadvector_no_alternatives(void) { return fals
static __always_inline bool has_xtheadvector(void) { return false; }
static inline bool riscv_v_first_use_handler(struct pt_regs *regs) { return false; }
static inline bool riscv_v_vstate_query(struct pt_regs *regs) { return false; }
-static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
#define riscv_v_vsize (0)
#define riscv_v_vstate_discard(regs) do {} while (0)
#define riscv_v_vstate_save(vstate, regs) do {} while (0)
@@ -435,6 +431,18 @@ static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
#endif /* CONFIG_RISCV_ISA_V */
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
+
+void riscv_v_vstate_ctrl_init(struct task_struct *tsk);
+bool riscv_v_vstate_ctrl_user_allowed(void);
+
+#else
+
+static inline void riscv_v_vstate_ctrl_init(struct task_struct *tsk) {}
+static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return true; }
+
+#endif /* CONFIG_RISCV_ISA_V_VSTATE_CTRL */
+
/*
* Return the implementation's vlen value.
*
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 9641343732782..b35d11ff3cc89 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -20,7 +20,9 @@
#include <asm/ptrace.h>
#include <asm/bug.h>
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
static bool riscv_v_implicit_uacc = true;
+#endif
static struct kmem_cache *riscv_v_user_cachep;
#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
static struct kmem_cache *riscv_v_kernel_cachep;
@@ -144,6 +146,8 @@ void riscv_v_thread_free(struct task_struct *tsk)
#endif
}
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
+
#define VSTATE_CTRL_GET_CUR(x) ((x) & PR_RISCV_V_VSTATE_CTRL_CUR_MASK)
#define VSTATE_CTRL_GET_NEXT(x) (((x) & PR_RISCV_V_VSTATE_CTRL_NEXT_MASK) >> 2)
#define VSTATE_CTRL_MAKE_NEXT(x) (((x) << 2) & PR_RISCV_V_VSTATE_CTRL_NEXT_MASK)
@@ -182,6 +186,8 @@ bool riscv_v_vstate_ctrl_user_allowed(void)
}
EXPORT_SYMBOL_GPL(riscv_v_vstate_ctrl_user_allowed);
+#endif
+
bool riscv_v_first_use_handler(struct pt_regs *regs)
{
u32 __user *epc = (u32 __user *)regs->epc;
@@ -227,6 +233,8 @@ bool riscv_v_first_use_handler(struct pt_regs *regs)
return true;
}
+#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
+
void riscv_v_vstate_ctrl_init(struct task_struct *tsk)
{
bool inherit;
@@ -330,3 +338,5 @@ static int __init riscv_v_init(void)
return riscv_v_sysctl_init();
}
core_initcall(riscv_v_init);
+
+#endif
--
2.52.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA
2026-10-07 8:51 [PATCH 0/3] riscv: Deprecate userspace vector control interfaces Samuel Holland
2026-10-07 8:51 ` [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE Samuel Holland
2026-10-07 8:51 ` [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl Samuel Holland
@ 2026-10-07 8:51 ` Samuel Holland
2026-10-13 16:58 ` Andy Chiu
2 siblings, 1 reply; 7+ messages in thread
From: Samuel Holland @ 2026-10-07 8:51 UTC (permalink / raw)
To: Paul Walmsley, Anup Patel, Atish Patra
Cc: Palmer Dabbelt, linux-kernel, kvm-riscv, linux-riscv, Andy Chiu,
Samuel Holland
The ability to prevent userspace from executing vector instructions was
provided as a escape hatch for software that was broken by adding vector
state to the signal context. This was hooked up to KVM so a process that
could not use V in userspace also could not create a KVM VM with V in
the ISA.
Remove this connection as it does not really help with any compatibility
concerns. A VMM that does not understand V will not include it in the
virtual machine's ISA.
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---
arch/riscv/kvm/isa.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/arch/riscv/kvm/isa.c b/arch/riscv/kvm/isa.c
index 971f44655100a..447c778bf850e 100644
--- a/arch/riscv/kvm/isa.c
+++ b/arch/riscv/kvm/isa.c
@@ -9,7 +9,6 @@
#include <linux/nospec.h>
#include <linux/pgtable.h>
#include <asm/kvm_isa.h>
-#include <asm/vector.h>
#define KVM_ISA_EXT_ARR(ext) \
[KVM_RISCV_ISA_EXT_##ext] = RISCV_ISA_EXT_##ext
@@ -159,8 +158,6 @@ bool kvm_riscv_isa_enable_allowed(unsigned long ext)
* Guest OS can use Svadu only when host OS enable Svadu.
*/
return arch_has_hw_pte_young();
- case KVM_RISCV_ISA_EXT_V:
- return riscv_v_vstate_ctrl_user_allowed();
default:
break;
}
--
2.52.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl
2026-10-07 8:51 ` [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl Samuel Holland
@ 2026-10-13 16:57 ` Andy Chiu
0 siblings, 0 replies; 7+ messages in thread
From: Andy Chiu @ 2026-10-13 16:57 UTC (permalink / raw)
To: Samuel Holland
Cc: Paul Walmsley, Anup Patel, Atish Patra, Palmer Dabbelt,
linux-kernel, kvm-riscv, linux-riscv
On Wed, Oct 07, 2026 at 01:51:17AM -0700, Samuel Holland wrote:
> The ability to prevent userspace from executing vector instructions was
> provided as a escape hatch for software that was broken by adding vector
> state to the signal context. This appears to be unused in practice, and
> creates confusion in the extension support returned by hwprobe(), as in
> this one special case an extension reported as present by hwprobe() is
> unusable.
>
> Since we believe it is safe to always allow vector usage, hide the prctl
> and sysctl behind a Kconfig option and mark them as deprecated, so they
> can be removed in the future. Note that significant userspace software
> like glibc already considers these controls explicitly unsupported.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Andy Chiu <tchiu@tenstorrent.com>
> ---
>
> arch/riscv/Kconfig | 10 ++++++++++
> arch/riscv/include/asm/processor.h | 4 +++-
> arch/riscv/include/asm/vector.h | 16 ++++++++++++----
> arch/riscv/kernel/vector.c | 10 ++++++++++
> 4 files changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e26450f0d38fb..83e52a0a85ba7 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -650,6 +650,16 @@ config RISCV_ISA_V
>
> If you don't know what to do here, say Y.
>
> +config RISCV_ISA_V_VSTATE_CTRL
> + bool "Deprecated prctl/sysctl for disallowing userspace vector access"
> + depends on RISCV_ISA_V
> + help
> + Add prctl and sysctl interfaces to disallow userspace to execute
> + vector instructions. These controls are deprecated because they create
> + ambiguity in the ISA extension availability reported by hwprobe.
> +
> + If you don't know what to do here, say N.
> +
> config RISCV_ISA_V_UCOPY_THRESHOLD
> int "Threshold size for vectorized user copies"
> depends on RISCV_ISA_V
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 815715c67f940..ad64df01417a2 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -121,7 +121,9 @@ struct thread_struct {
> unsigned long envcfg;
> unsigned long sum;
> u32 riscv_v_flags;
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> u32 vstate_ctrl;
> +#endif
> struct __riscv_v_ext_state vstate;
> unsigned long align_ctl;
> struct __riscv_v_ext_state kernel_vstate;
> @@ -202,7 +204,7 @@ extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src
>
> extern unsigned long signal_minsigstksz __ro_after_init;
>
> -#ifdef CONFIG_RISCV_ISA_V
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> /* Userspace interface for PR_RISCV_V_{SET,GET}_VS prctl()s: */
> #define RISCV_V_SET_CONTROL(arg) riscv_v_vstate_ctrl_set_current(arg)
> #define RISCV_V_GET_CONTROL() riscv_v_vstate_ctrl_get_current()
nit: consider changing the enclosing CONFIG_RISCV_ISA_V at the comment to
CONFIG_RISCV_ISA_V_VSTATE_CTRL if this needs respin.
> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
> index fffe72a772080..5425a25f8a196 100644
> --- a/arch/riscv/include/asm/vector.h
> +++ b/arch/riscv/include/asm/vector.h
> @@ -404,9 +404,6 @@ static inline void __switch_to_vector(struct task_struct *prev,
> }
> }
>
> -void riscv_v_vstate_ctrl_init(struct task_struct *tsk);
> -bool riscv_v_vstate_ctrl_user_allowed(void);
> -
> #else /* ! CONFIG_RISCV_ISA_V */
>
> struct pt_regs;
> @@ -418,7 +415,6 @@ static __always_inline bool has_xtheadvector_no_alternatives(void) { return fals
> static __always_inline bool has_xtheadvector(void) { return false; }
> static inline bool riscv_v_first_use_handler(struct pt_regs *regs) { return false; }
> static inline bool riscv_v_vstate_query(struct pt_regs *regs) { return false; }
> -static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
> #define riscv_v_vsize (0)
> #define riscv_v_vstate_discard(regs) do {} while (0)
> #define riscv_v_vstate_save(vstate, regs) do {} while (0)
> @@ -435,6 +431,18 @@ static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
>
> #endif /* CONFIG_RISCV_ISA_V */
>
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> +
> +void riscv_v_vstate_ctrl_init(struct task_struct *tsk);
> +bool riscv_v_vstate_ctrl_user_allowed(void);
> +
> +#else
> +
> +static inline void riscv_v_vstate_ctrl_init(struct task_struct *tsk) {}
> +static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return true; }
> +
> +#endif /* CONFIG_RISCV_ISA_V_VSTATE_CTRL */
> +
> /*
> * Return the implementation's vlen value.
> *
> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
> index 9641343732782..b35d11ff3cc89 100644
> --- a/arch/riscv/kernel/vector.c
> +++ b/arch/riscv/kernel/vector.c
> @@ -20,7 +20,9 @@
> #include <asm/ptrace.h>
> #include <asm/bug.h>
>
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> static bool riscv_v_implicit_uacc = true;
> +#endif
> static struct kmem_cache *riscv_v_user_cachep;
> #ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
> static struct kmem_cache *riscv_v_kernel_cachep;
> @@ -144,6 +146,8 @@ void riscv_v_thread_free(struct task_struct *tsk)
> #endif
> }
>
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> +
> #define VSTATE_CTRL_GET_CUR(x) ((x) & PR_RISCV_V_VSTATE_CTRL_CUR_MASK)
> #define VSTATE_CTRL_GET_NEXT(x) (((x) & PR_RISCV_V_VSTATE_CTRL_NEXT_MASK) >> 2)
> #define VSTATE_CTRL_MAKE_NEXT(x) (((x) << 2) & PR_RISCV_V_VSTATE_CTRL_NEXT_MASK)
> @@ -182,6 +186,8 @@ bool riscv_v_vstate_ctrl_user_allowed(void)
> }
> EXPORT_SYMBOL_GPL(riscv_v_vstate_ctrl_user_allowed);
>
> +#endif
> +
> bool riscv_v_first_use_handler(struct pt_regs *regs)
> {
> u32 __user *epc = (u32 __user *)regs->epc;
> @@ -227,6 +233,8 @@ bool riscv_v_first_use_handler(struct pt_regs *regs)
> return true;
> }
>
> +#ifdef CONFIG_RISCV_ISA_V_VSTATE_CTRL
> +
> void riscv_v_vstate_ctrl_init(struct task_struct *tsk)
> {
> bool inherit;
> @@ -330,3 +338,5 @@ static int __init riscv_v_init(void)
> return riscv_v_sysctl_init();
> }
> core_initcall(riscv_v_init);
> +
> +#endif
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA
2026-10-07 8:51 ` [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA Samuel Holland
@ 2026-10-13 16:58 ` Andy Chiu
0 siblings, 0 replies; 7+ messages in thread
From: Andy Chiu @ 2026-10-13 16:58 UTC (permalink / raw)
To: Samuel Holland
Cc: Paul Walmsley, Anup Patel, Atish Patra, Palmer Dabbelt,
linux-kernel, kvm-riscv, linux-riscv
On Wed, Oct 07, 2026 at 01:51:18AM -0700, Samuel Holland wrote:
> The ability to prevent userspace from executing vector instructions was
> provided as a escape hatch for software that was broken by adding vector
> state to the signal context. This was hooked up to KVM so a process that
> could not use V in userspace also could not create a KVM VM with V in
> the ISA.
>
> Remove this connection as it does not really help with any compatibility
> concerns. A VMM that does not understand V will not include it in the
> virtual machine's ISA.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Andy Chiu <tchiu@tenstorrent.com>
> ---
>
> arch/riscv/kvm/isa.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/arch/riscv/kvm/isa.c b/arch/riscv/kvm/isa.c
> index 971f44655100a..447c778bf850e 100644
> --- a/arch/riscv/kvm/isa.c
> +++ b/arch/riscv/kvm/isa.c
> @@ -9,7 +9,6 @@
> #include <linux/nospec.h>
> #include <linux/pgtable.h>
> #include <asm/kvm_isa.h>
> -#include <asm/vector.h>
>
> #define KVM_ISA_EXT_ARR(ext) \
> [KVM_RISCV_ISA_EXT_##ext] = RISCV_ISA_EXT_##ext
> @@ -159,8 +158,6 @@ bool kvm_riscv_isa_enable_allowed(unsigned long ext)
> * Guest OS can use Svadu only when host OS enable Svadu.
> */
> return arch_has_hw_pte_young();
> - case KVM_RISCV_ISA_EXT_V:
> - return riscv_v_vstate_ctrl_user_allowed();
> default:
> break;
> }
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE
2026-10-07 8:51 ` [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE Samuel Holland
@ 2026-10-13 16:59 ` Andy Chiu
0 siblings, 0 replies; 7+ messages in thread
From: Andy Chiu @ 2026-10-13 16:59 UTC (permalink / raw)
To: Samuel Holland
Cc: Paul Walmsley, Anup Patel, Atish Patra, Palmer Dabbelt,
linux-kernel, kvm-riscv, linux-riscv
On Wed, Oct 07, 2026 at 01:51:16AM -0700, Samuel Holland wrote:
> The ability to prevent userspace from executing vector instructions was
> provided as a escape hatch for software that was broken by adding vector
> state to the signal context. This appears to be unused in practice, and
> creates confusion in the extension support returned by hwprobe(), as in
> this one special case an extension reported as present by hwprobe() is
> unusable.
>
> Since we believe it is safe to always allow vector usage, start removing
> this functionality by dropping the Kconfig option. It is possible to get
> equivalent behavior by setting the sysctl at boot via the kernel command
> line, but that method will also soon be deprecated.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Andy Chiu <tchiu@tenstorrent.com>
Thanks!
> ---
>
> arch/riscv/Kconfig | 11 -----------
> arch/riscv/kernel/vector.c | 2 +-
> 2 files changed, 1 insertion(+), 12 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index d6c2dbf8455ce..e26450f0d38fb 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -650,17 +650,6 @@ config RISCV_ISA_V
>
> If you don't know what to do here, say Y.
>
> -config RISCV_ISA_V_DEFAULT_ENABLE
> - bool "Enable userspace Vector by default"
> - depends on RISCV_ISA_V
> - default y
> - help
> - Say Y here if you want to enable Vector in userspace by default.
> - Otherwise, userspace has to make explicit prctl() call to enable
> - Vector, or enable it via the sysctl interface.
> -
> - If you don't know what to do here, say Y.
> -
> config RISCV_ISA_V_UCOPY_THRESHOLD
> int "Threshold size for vectorized user copies"
> depends on RISCV_ISA_V
> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
> index b112166d51e9f..9641343732782 100644
> --- a/arch/riscv/kernel/vector.c
> +++ b/arch/riscv/kernel/vector.c
> @@ -20,7 +20,7 @@
> #include <asm/ptrace.h>
> #include <asm/bug.h>
>
> -static bool riscv_v_implicit_uacc = IS_ENABLED(CONFIG_RISCV_ISA_V_DEFAULT_ENABLE);
> +static bool riscv_v_implicit_uacc = true;
> static struct kmem_cache *riscv_v_user_cachep;
> #ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
> static struct kmem_cache *riscv_v_kernel_cachep;
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2026-10-13 16:59 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-10-07 8:51 [PATCH 0/3] riscv: Deprecate userspace vector control interfaces Samuel Holland
2026-10-07 8:51 ` [PATCH 1/3] riscv: Drop CONFIG_RISCV_ISA_V_DEFAULT_ENABLE Samuel Holland
2026-10-13 16:59 ` Andy Chiu
2026-10-07 8:51 ` [PATCH 2/3] riscv: Deprecate vector state prctl/sysctl Samuel Holland
2026-10-13 16:57 ` Andy Chiu
2026-10-07 8:51 ` [PATCH 3/3] RISC-V: KVM: Decouple vector prctl state from VM ISA Samuel Holland
2026-10-13 16:58 ` Andy Chiu
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