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KVM: selftests: Do not intercept #PF by default in nVMX tests

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init_vmcs_control_fields() sets PFEC_MASK and PFEC_MATCH so that they
never match, which reverses the meaning of the PF_VECTOR bit in
EXCEPTION_BITMAP (which is zeroed), effectively enabling #PF
interception by default.

The relevant part of the SDM describes this:

  When a page fault occurs, a processor consults (1) bit 14 of the
  exception bitmap; (2) the error code produced with the page fault [PFEC];
  (3) the page-fault error-code mask field [PFEC_MASK]; and (4) the
  page-fault error-code match field [PFEC_MATCH].

  It checks if PFEC & PFEC_MASK = PFEC_MATCH.  If there is equality, the
  specification of bit 14 in the exception bitmap is followed (for example,
  a VM exit occurs if that bit is set). If there is inequality, the meaning
  of that bit is reversed (for example, a VM exit occurs if that bit is
  clear).

Clear PFEC_MATCH such that there is equality, and the #PF bit in the
exception bitmap is followed, so that #PFs are not intercepted by default,
same as every other exception.  This also allows tests to set the #PF bit
in the exception bitmap if they want to intercept #PFs, without having to
muck with the PFEC_{MASK,MATCH} fields.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260728174232.2423257-10-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yosry Ahmed 2026-07-28 17:42:28 +00:00 committed by Sean Christopherson
parent e21d4dc0ca
commit 7317f5b143
1 changed files with 1 additions and 1 deletions
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2
tools/testing/selftests/kvm/lib/x86/vmx.c
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@ -232,7 +232,7 @@ static inline void init_vmcs_control_fields(struct vmx_pages *vmx)
vmwrite(EXCEPTION_BITMAP, 0);
vmwrite(PAGE_FAULT_ERROR_CODE_MASK, 0);
vmwrite(PAGE_FAULT_ERROR_CODE_MATCH, -1); /* Never match */
vmwrite(PAGE_FAULT_ERROR_CODE_MATCH, 0);
vmwrite(CR3_TARGET_COUNT, 0);
vmwrite(VM_EXIT_CONTROLS, rdmsr(MSR_IA32_VMX_EXIT_CTLS) |
VM_EXIT_HOST_ADDR_SPACE_SIZE); /* 64-bit host */