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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 23/09/2026 17:27, Suzuki K Poulose wrote:
> On 23/09/2026 14:23, 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())                         \

This needs to be :
			  if (is_nvhe_hyp_code() && !is_protected_kvm_enabled())

>> +                               __kvm = kern_hyp_va(__kvm);             \

Otherwise, we unnecessarily convert the vcpu->kvm for a hyp_vcpu and
that is not going to end well for pKVM.

Cheers
Suzuki


>> +                       __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;                                            \
>> +        })
>>
>>   #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, that works and looks neat. I will incorporate it.
> 
> Cheers
> Suzuki
> 
>> Thanks,
>> Gavin
>>
>