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KVM: x86: Zero XSTATE components on INIT by iterating over supported features

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Tweak the code a bit to facilitate resetting more xstate components in
the future, e.g., CET's xstate-managed MSRs.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Link: https://lore.kernel.org/r/20250812025606.74625-6-chao.gao@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Chao Gao 2025-08-11 19:55:13 -07:00 committed by Sean Christopherson
parent 41f6710f99
commit c26675447f
1 changed files with 9 additions and 3 deletions
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12
arch/x86/kvm/x86.c
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@ -12401,6 +12401,8 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
static void kvm_xstate_reset(struct kvm_vcpu *vcpu, bool init_event)
{
struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
u64 xfeatures_mask;
int i;
/*
* Guest FPU state is zero allocated and so doesn't need to be manually
@ -12414,16 +12416,20 @@ static void kvm_xstate_reset(struct kvm_vcpu *vcpu, bool init_event)
* are unchanged. Currently, the only components that are zeroed and
* supported by KVM are MPX related.
*/
if (!kvm_mpx_supported())
xfeatures_mask = (kvm_caps.supported_xcr0 | kvm_caps.supported_xss) &
(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
if (!xfeatures_mask)
return;
BUILD_BUG_ON(sizeof(xfeatures_mask) * BITS_PER_BYTE <= XFEATURE_MAX);
/*
* All paths that lead to INIT are required to load the guest's FPU
* state (because most paths are buried in KVM_RUN).
*/
kvm_put_guest_fpu(vcpu);
fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
for_each_set_bit(i, (unsigned long *)&xfeatures_mask, XFEATURE_MAX)
fpstate_clear_xstate_component(fpstate, i);
kvm_load_guest_fpu(vcpu);
}