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SubjectRe: [PATCH v2 3/3] KVM: SVM: WARN if GATag generation drops VM or vCPU ID information
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On 2/7/2023 7:21 AM, Sean Christopherson wrote:
> WARN if generating a GATag given a VM ID and vCPU ID doesn't yield the
> same IDs when pulling the IDs back out of the tag. Don't bother adding
> error handling to callers, this is very much a paranoid sanity check as
> KVM fully controls the VM ID and is supposed to reject too-big vCPU IDs.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/avic.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 326341a22153..cfc8ab773025 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -43,12 +43,21 @@
> #define AVIC_VM_ID_SHIFT HWEIGHT32(AVIC_PHYSICAL_MAX_INDEX_MASK)
> #define AVIC_VM_ID_MASK (GENMASK(31, AVIC_VM_ID_SHIFT) >> AVIC_VM_ID_SHIFT)
>
> -#define AVIC_GATAG(x, y) (((x & AVIC_VM_ID_MASK) << AVIC_VM_ID_SHIFT) | \
> - (y & AVIC_VCPU_ID_MASK))
> #define AVIC_GATAG_TO_VMID(x) ((x >> AVIC_VM_ID_SHIFT) & AVIC_VM_ID_MASK)
> #define AVIC_GATAG_TO_VCPUID(x) (x & AVIC_VCPU_ID_MASK)
>
> -static_assert(AVIC_GATAG(AVIC_VM_ID_MASK, AVIC_VCPU_ID_MASK) == -1u);
> +#define __AVIC_GATAG(vm_id, vcpu_id) ((((vm_id) & AVIC_VM_ID_MASK) << AVIC_VM_ID_SHIFT) | \
> + ((vcpu_id) & AVIC_VCPU_ID_MASK))
> +#define AVIC_GATAG(vm_id, vcpu_id) \
> +({ \
> + u32 ga_tag = __AVIC_GATAG(vm_id, vcpu_id); \
> + \
> + WARN_ON_ONCE(AVIC_GATAG_TO_VCPUID(ga_tag) != (vcpu_id)); \
> + WARN_ON_ONCE(AVIC_GATAG_TO_VMID(ga_tag) != (vm_id)); \
> + ga_tag; \
> +})
> +
> +static_assert(__AVIC_GATAG(AVIC_VM_ID_MASK, AVIC_VCPU_ID_MASK) == -1u);
>
> static bool force_avic;
> module_param_unsafe(force_avic, bool, 0444);

Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

Thanks,
Suravee

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