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Diffstat (limited to 'arch/x86/include/asm/kvm_host.h')
-rw-r--r--arch/x86/include/asm/kvm_host.h16
1 files changed, 13 insertions, 3 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4dffbc10d3f8..40a0c0fd95ca 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -781,9 +781,19 @@ struct kvm_vcpu_arch {
u64 msr_kvm_poll_control;
/*
- * Indicate whether the access faults on its page table in guest
- * which is set when fix page fault and used to detect unhandeable
- * instruction.
+ * Indicates the guest is trying to write a gfn that contains one or
+ * more of the PTEs used to translate the write itself, i.e. the access
+ * is changing its own translation in the guest page tables. KVM exits
+ * to userspace if emulation of the faulting instruction fails and this
+ * flag is set, as KVM cannot make forward progress.
+ *
+ * If emulation fails for a write to guest page tables, KVM unprotects
+ * (zaps) the shadow page for the target gfn and resumes the guest to
+ * retry the non-emulatable instruction (on hardware). Unprotecting the
+ * gfn doesn't allow forward progress for a self-changing access because
+ * doing so also zaps the translation for the gfn, i.e. retrying the
+ * instruction will hit a !PRESENT fault, which results in a new shadow
+ * page and sends KVM back to square one.
*/
bool write_fault_to_shadow_pgtable;