KVM: SVM: Fix nested NPF injection of PFERR_GUEST_{PAGE,FINAL}_MASK bits

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Fix KVM's generation of PFERR_GUEST_{PAGE,FINAL}_MASK bits when injecting a
Nested Page Fault into L1.  Currently, KVM blindly stuffs GUEST_FINAL into
L1, which is blatantly wrong given that KVM obviously generates NPFs for
page table accesses.

There are two paths that trigger NPF injection: hardware NPF exits (from
L2) and emulation-triggered faults, i.e. when KVM detects a NPF as part of
emulating an L2 GVA access.  For the hardware case, use the bits verbatim
from the VMCB, as KVM is simply forwarding a NPF to L1.  For the emulation
case, propagate the GUEST_{PAGE,FINAL} bits from the access field (which
were recently added for MBEC+GMET support).

To differentiate between the two cases, add "hardware_nested_page_fault"
to "struct x86_exception", and set it when injecting a NPF in response to
an NPF exit from L2.

To help guard against future goofs, assert that exactly one of GUEST_PAGE
or GUEST_FINAL is set when injecting a NPF.  Unlike VMX, there are no
(known) cases where hardware doesn't set either bit, and KVM should always
set one or the other when emulating a GVA access.

Signed-off-by: Kevin Cheng <chengkev@google.com>
[sean: use plumbed in @access bits, massage changelog]
Link: https://patch.msgid.link/20260522232701.3671446-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

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This commit is contained in:

Kevin Cheng 2026-05-22 16:26:59 -07:00 • committed by Sean Christopherson

parent fe0b872d75

commit 297c2fe249

3 changed files with 31 additions and 21 deletions

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2

arch/x86/include/asm/kvm_host.h

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15

arch/x86/kvm/mmu/paging_tmpl.h

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35

arch/x86/kvm/svm/nested.c

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