• Brijesh Singh's avatar
    KVM: SVM: Limit PFERR_NESTED_GUEST_PAGE error_code check to L1 guest · 9d7960e0
    Brijesh Singh authored
    commit 64531a3b upstream.
    
    Commit 14727754 ("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: 14727754
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Radim Krčmář <rkrcmar@redhat.com>
    Cc: Thomas Lendacky <thomas.lendacky@amd.com>
    Signed-off-by: default avatarBrijesh Singh <brijesh.singh@amd.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    9d7960e0
mmu.c 138 KB