Re: [PATCH v19 05/20] KVM: arm64: Track the type of VM in kvm_arch

[Gavin Shan <gshan@redhat.com>]

On 9/23/26 11:23 PM, Gavin Shan wrote:
> On 9/23/26 8:24 PM, Suzuki K Poulose wrote:
>> On 23/09/2026 07:19, Gavin Shan wrote:
>>> On 9/23/26 4:05 PM, Gavin Shan wrote:
>>>> On 9/21/26 7:28 AM, Suzuki K Poulose wrote:
>>>>> KVM arm64 has different types of VMs with all the different modes in which
>>>>> the hypervisor code can be run. e.g., VHE, nVHE, pKVM etc. Then there is
>>>>> protected VM and normal VMs with pKVM. We might soon add other types,
>>>>> e.g., Arm CCA Realm. So in an effort to make the handling of these
>>>>> different types of VMs a bit more friendly to the eyes, add a VM flavor to
>>>>> the kvm_arch and we could then add handlers for different operations based
>>>>> on the VM type.
>>>>>
>>>>> Keep the flavor initialisation at the beginning to allow for the detection
>>>>> early enough and fail out on any unsupported requests.
>>>>>
>>>>> With that, add wrappers for checking the "type" of a VM and replace the
>>>>> existing users with the new wrappers.
>>>>>
>>>>> Given we already have the construct of "kvm_vm_is_protected" in the core
>>>>> KVM code, use that for all confidential compute guests including Realms
>>>>> that we are about to add.
>>>>>
>>>>> Adds __VM_PROTECTED marker vm flavor to generalize kvm_vm_is_protected()
>>>>> to predicate all confidential guests running on KVM. In later patches, we
>>>>> would add Realm VMs, which would also be classified as protected.
>>>>>
>>>>> Add explicit helper to detect if a given VM is a "protected" VM under pKVM.
>>>>> Change the existing users that precisely want to check the VM type. These
>>>>> include :
>>>>>    - kvm_arch_prepare_memory_region - For preventing memslot changes after
>>>>>      pVM creation.
>>>>>
>>>>> All the others are retained as a wider check for confidential guest VMs.
>>>>> These are:
>>>>>   - kvm_vm_ioctl_set_counter_offset - For disallowing timer offset
>>>>>     configuration
>>>>>   - io_mem_abort for dabt handling without valid syndrome information
>>>>>
>>>>> Both of which are true for Realms too.
>>>>>
>>>>> Realms support is restricted to VHE host and thus "kvm_vm_is_protected()"
>>>>> checks in the pkvm hyp specific code doesn't need to change, as the only
>>>>> protected guests it deals with is "protected pKVM" guests. To tighten this
>>>>> init_pkvm_hyp_vm() restricts the hyp copy of the vm_flavor to the ones it
>>>>> supports.
>>>>>
>>>>> Suggested-by: Marc Zyngier <maz@kernel.org>
>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>>>> ---
>>>>> Changes since v18:
>>>>>   - Merge the __VM_PROTECTED marker and the widening of kvm_vm_is_protected()
>>>>>     to this patch.
>>>>>   - Merge the use of kvm_vm_is_unprotected_pkvm() for ! kvm_vm_is_protected()
>>>>>     given the scope changes here.
>>>>>   - Drop Fuad's review tag, as this patch has multiple merges
>>>>>   - Restrict the VM flavors to the supported types in init_pkvm_hyp_vm().
>>>>>   - Drop kvm_vm_hyp_is_pkvm() and revert to is_protected_kvm_enabled()
>>>>>   - Use is_protected_kvm_enabled() to make the pKVM guest flavor checks.
>>>>>   - s/PKVM/pKVM for commit descriptions too
>>>>>
>>>>> Changes since v17:
>>>>>   * s/PKVM/pKVM for the comments
>>>>>   * Drop type argument for pkvm_init_host_vm and also drop protected variable.
>>>>>   * Add helpers for checking if the VM is running on pKVM (kvm_vm_hyp_is_pkvm())
>>>>>   * Use kvm_vm_hyp_is_pkvm() to replace is_protected_kvm_enabled() with valid
>>>>>     kvm instance
>>>>> ---
>>>>>   arch/arm64/include/asm/kvm_host.h | 22 +++++++++++++++++++---
>>>>>   arch/arm64/include/asm/kvm_pkvm.h |  4 ++--
>>>>>   arch/arm64/kvm/arm.c              | 31 ++++++++++++++++++++++++++-----
>>>>>   arch/arm64/kvm/handle_exit.c      |  2 +-
>>>>>   arch/arm64/kvm/hyp/nvhe/pkvm.c    |  6 +++++-
>>>>>   arch/arm64/kvm/mmu.c              |  2 +-
>>>>>   arch/arm64/kvm/pkvm.c             |  6 ++----
>>>>>   7 files changed, 56 insertions(+), 17 deletions(-)
>>>>>
>>>>
>>>> This causes broken nVHE mode. I applied PATCH[01-05] to v7.3.rc4 whose head commit
>>>> is f0100363d8c3, and kselftests/kvm/guest_print causes host crash (as below). I don't
>>>> see the crash if only PATCH[01-04] are applied.
>>>>
>>>> host$ cat /proc/cmdline | grep kvm-arm\.mode
>>>> BOOT_IMAGE=(hd0,gpt2)/vmlinuz-7.3.0-rc4-gavin+ root=/dev/mapper/ rhel_nvidia--grace--hopper--01-root ro crashkernel=2G-4G:406M,4G-64G:470M,64G-:726M rd.lvm.lv=rhel_nvidia- grace-hopper-01/root rd.lvm.lv=rhel_nvidia-grace-hopper-01/swap video=simplefb:off kvm-arm.mode=nvhe
>>>>
>>>> host$ cd linux/tools/testing/selftests/kvm
>>>> host$ ./guest_print_test
>>>> Random seed: 0x193a0ed3
>>>> [  192.754328] kvm [6674]: nVHE hyp panic at: [<ffff8000811da044>] __kvm_nvhe___timer_enable_traps+0x4/0x160!
>>>> [  192.754338] kvm [6674]: nVHE call trace:
>>>> [  192.754339] kvm [6674]:  [<ffff8000811dcf34>] __kvm_nvhe_hyp_panic+0xb4/0xe0
>>>> [  192.754342] kvm [6674]:  [<ffff8000811dcba4>] __kvm_nvhe___kvm_vcpu_run+0x164/0x440
>>>> [  192.754344] kvm [6674]:  [<ffff8000811dfe90>] __kvm_nvhe_handle___kvm_vcpu_run+0x40/0x1f0
>>>> [  192.754346] kvm [6674]:  [<ffff8000811e0238>] __kvm_nvhe_handle_trap+0x158/0x280
>>>> [  192.754347] kvm [6674]:  [<ffff8000811dd8fc>] __kvm_nvhe___skip_pauth_save+0x4/0x4
>>>> [  192.754348] kvm [6674]: ---[ end nVHE call trace ]---
>>>> [  192.754350] Code: d2818002 17fffff7 d503201f f9400001 (b94a6821)
>>>> [  192.754350] kvm [6674]: Hyp Offset: 0xfffeb0d7fe2e0000
>>>> [  192.754351] Kernel panic - not syncing: HYP panic:
>>>> [  192.754351] PS:834003c9 PC:0000cf2882efa044 ESR:0000000096000004
>>>> [  192.754351] FAR:ffff00009b286a68 HPFAR:8000000000000000 PAR:1d00ec7edbadc8de
>>>> [  192.754351] VCPU:0000cf011848a350
>>>> [  192.845154] CPU: 12 UID: 0 PID: 6674 Comm: guest_print_tes Kdump: loaded Not tainted 7.3.0-rc4-gavin+ #7 PREEMPT(full)
>>>> [  192.856182] Hardware name:  GH200 P5042, BIOS 02.04.01 20250422
>>>> [  192.862231] Call trace:
>>>> [  192.864725]  show_stack+0x20/0x38 (C)
>>>> [  192.868471]  dump_stack_lvl+0x88/0xb8
>>>> [  192.872215]  dump_stack+0x18/0x30
>>>> [  192.875598]  vpanic+0x280/0x498
>>>> [  192.878806]  panic+0x68/0x70
>>>> [  192.881745]  nvhe_hyp_panic_handler+0x184/0x190
>>>> [  192.886372]  kvm_arm_vcpu_enter_exit+0x24/0x100
>>>> [  192.891003]  kvm_arch_vcpu_ioctl_run+0x254/0x7c0
>>>> [  192.895726]  kvm_vcpu_ioctl+0x174/0xb40
>>>> [  192.899645]  __arm64_sys_ioctl+0xb0/0x120
>>>> [  192.903745]  invoke_syscall.constprop.0+0xa8/0x100
>>>> [  192.908639]  do_el0_svc+0xb8/0xe0
>>>> [  192.912022]  el0_svc+0x48/0x1f8
>>>> [  192.915228]  el0t_64_sync_handler+0xa0/0xe8
>>>> [  192.919500]  el0t_64_sync+0x1ac/0x1b0
>>>> [  192.923243] SMP: stopping secondary CPUs
>>>> [  192.927653] Starting crashdump kernel...
>>>> [  192.931658] Bye!
>>>>
>>>
>>> With the following changes applied after PATCH[01-05] on top of v7.3.rc4, the crash
>>> is avoided.
>>>
>>> In arch/arm64/include/asm/kvm_host.h:
>>>
>>> -#define kvm_vm_is_protected(kvm)       ((kvm)->arch.vm_flavor >= __VM_PROTECTED)
>>> +#define kvm_vm_is_protected(kvm)       \
>>> +       (is_protected_kvm_enabled() && (kvm)->arch.vm_flavor >= __VM_PROTECTED)
>>
>> That only papers over the problem. We can't use the vcpu_is_*
>> constructs from nvhe hyp, without converting the vcpu->kvm to
>> the hyp address, before accessing it. The fix is a bit more
>> involved. One option is to define the vcpu_is_* helpers only
>> for the !NVHE hyp code in the kvm_host.h (to avoid pulling
>> in the asm/kvm_mmu.h in to kvm_host.h and then make a mess
>> with header dependencies) and define the NVHE version in
>> asm/kvm_hyp.h. Something like :
>>
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 46a7f6c1e426c..4016d09ed39c3 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -1545,11 +1545,14 @@ struct kvm *kvm_arch_alloc_vm(void);
>>   #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
>>
>>   #define kvm_vm_is_protected(kvm)       ((kvm)->arch.vm_flavor >= __VM_PROTECTED)
>> +
>> +#ifndef __KVM_NVHE_HYPERVISOR__
>>   #define vcpu_is_protected(vcpu) kvm_vm_is_protected((vcpu)->kvm)
>> +#define vcpu_is_protected_pkvm(vcpu) kvm_vm_is_protected_pkvm((vcpu)->kvm)
>> +#endif
>>
>>   #define kvm_vm_is_protected_pkvm(kvm)          \
>>          (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor == VM_PROTECTED_PKVM))
>> -#define vcpu_is_protected_pkvm(vcpu)   kvm_vm_is_protected_pkvm(vcpu->kvm)
>>
>>   #define kvm_vm_is_unprotected_pkvm(kvm)                \
>>          (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor == VM_PKVM))
>> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
>> index 4974492744cc8..3bf87e81af430 100644
>> --- a/arch/arm64/include/asm/kvm_hyp.h
>> +++ b/arch/arm64/include/asm/kvm_hyp.h
>> @@ -137,6 +137,19 @@ int __pkvm_init(phys_addr_t phys, unsigned long size, unsigned long *per_cpu_bas
>>   void __noreturn __host_enter(struct kvm_cpu_context *host_ctxt);
>>   #endif
>>
>> +#ifdef __KVM_NVHE_HYPERVISOR__
>> +#define vcpu_is_protected(vcpu)        \
>> +       ({                                                              \
>> +               struct kvm *__kvm = READ_ONCE((vcpu)->kvm);             \
>> +               __kvm && kvm_vm_is_protected((kern_hyp_va(__kvm)));     \
>> +       })
>> +#define vcpu_is_protected_pkvm(vcpu)                                   \
>> +       ({                                                              \
>> +               struct kvm *__kvm = READ_ONCE((vcpu)->kvm);             \
>> +               __kvm && kvm_vm_is_protected_pkvm((kern_hyp_va(__kvm)));\
>> +       })
>> +#endif
>> +
>>
>>
>> Or explicitly convert all nvhe accessors to a new "nvhe_vcpu_is_protected"
>>
>> The second one sounds like a better option to me.
>>
> 
> We just need to include "asm/kvm_mmu.h" to "arch/arm64/mmio.c". With it,
> we can have unified functions (macros) in kvm_host.h to accomodate all
> cases, like below.
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9b1cf9c59e81..b9c9a9f203f9 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1514,11 +1514,36 @@ struct kvm *kvm_arch_alloc_vm(void);
>   #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
> 
>   #define kvm_vm_is_protected(kvm)       ((kvm)->arch.vm_flavor >= __VM_PROTECTED)
> -#define vcpu_is_protected(vcpu)                kvm_vm_is_protected((vcpu)->kvm)
> +#define vcpu_is_protected(vcpu)                                                \
> +       ({                                                              \
> +               struct kvm *__kvm = READ_ONCE((vcpu)->kvm);             \
> +               bool __protected = false;                               \
> +                                                                       \
> +               if (__kvm) {                                            \
> +                       if (is_nvhe_hyp_code())                         \
> +                               __kvm = kern_hyp_va(__kvm);             \
> +                       __protected = kvm_vm_is_protected(__kvm);       \
> +               }                                                       \
> +                                                                       \
> +               __protected;                                            \
> +        })
> +
> 
>   #define kvm_vm_is_protected_pkvm(kvm)          \
>          (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor == VM_PROTECTED_PKVM))
> -#define vcpu_is_protected_pkvm(vcpu)   kvm_vm_is_protected_pkvm(vcpu->kvm)
> +#define vcpu_is_protected_pkvm(vcpu)                                   \
> +       ({                                                              \
> +               struct kvm *__kvm = READ_ONCE((vcpu)->kvm);             \
> +               bool __protected = false;                               \
> +                                                                       \
> +               if (__kvm) {                                            \
> +                       if (is_nvhe_hyp_code())                         \
> +                               __kvm = kern_hyp_va(__kvm);             \
> +                       __protected = kvm_vm_is_protected_pkvm(__kvm);  \
> +               }                                                       \
> +                                                                       \
> +               __protected;                                            \
> +        })
> 

Besides, vcpu_is_protected_pkvm() isn't used anywhere in branch "cca/cca-host/kvm-v19/integration",
so it can be removed :)


>   #define kvm_vm_is_unprotected_pkvm(kvm)                \
>          (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor == VM_PKVM))
> diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
> index d1c3a352d5a2..ab1d2fef9a52 100644
> --- a/arch/arm64/kvm/mmio.c
> +++ b/arch/arm64/kvm/mmio.c
> @@ -6,6 +6,7 @@
> 
>   #include <linux/kvm_host.h>
>   #include <asm/kvm_emulate.h>
> +#include <asm/kvm_mmu.h>
>   #include <trace/events/kvm.h>
> 
>   #include "trace.h"
> 
> Thanks,
> Gavin