This is a note to let you know that I've just added the patch titled KVM: SVM: Limit PFERR_NESTED_GUEST_PAGE error_code check to L1 guest to the 4.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-svm-limit-pferr_nested_guest_page-error_code-check-to-l1-guest.patch and it can be found in the queue-4.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 64531a3b70b17c8d3e77f2e49e5e1bb70f571266 Mon Sep 17 00:00:00 2001 From: Brijesh Singh <brijesh.singh@xxxxxxx> Date: Mon, 7 Aug 2017 14:11:30 -0500 Subject: KVM: SVM: Limit PFERR_NESTED_GUEST_PAGE error_code check to L1 guest MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Brijesh Singh <brijesh.singh@xxxxxxx> commit 64531a3b70b17c8d3e77f2e49e5e1bb70f571266 upstream. Commit 147277540bbc ("kvm: svm: Add support for additional SVM NPF error codes", 2016-11-23) added a new error code to aid nested page fault handling. The commit unprotects (kvm_mmu_unprotect_page) the page when we get a NPF due to guest page table walk where the page was marked RO. However, if an L0->L2 shadow nested page table can also be marked read-only when a page is read only in L1's nested page table. If such a page is accessed by L2 while walking page tables it can cause a nested page fault (page table walks are write accesses). However, after kvm_mmu_unprotect_page we may get another page fault, and again in an endless stream. To cover this use case, we qualify the new error_code check with vcpu->arch.mmu_direct_map so that the error_code check would run on L1 guest, and not the L2 guest. This avoids hitting the above scenario. Fixes: 147277540bbc54119172481c8ef6d930cc9fbfc2 Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> Cc: Thomas Lendacky <thomas.lendacky@xxxxxxx> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/mmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4759,7 +4759,8 @@ int kvm_mmu_page_fault(struct kvm_vcpu * * Note: AMD only (since it supports the PFERR_GUEST_PAGE_MASK used * in PFERR_NEXT_GUEST_PAGE) */ - if (error_code == PFERR_NESTED_GUEST_PAGE) { + if (vcpu->arch.mmu.direct_map && + error_code == PFERR_NESTED_GUEST_PAGE) { kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(cr2)); return 1; } Patches currently in stable-queue which might be from brijesh.singh@xxxxxxx are queue-4.12/kvm-svm-limit-pferr_nested_guest_page-error_code-check-to-l1-guest.patch