On Mon, Aug 22, 2016 at 07:23:44PM -0400, Brijesh Singh wrote: > From: Tom Lendacky <thomas.lendacky@xxxxxxx> > > AMD hardware adds two additional bits to aid in nested page fault handling. > > Bit 32 - NPF occurred while translating the guest's final physical address > Bit 33 - NPF occurred while translating the guest page tables > > The guest page tables fault indicator can be used as an aid for nested > virtualization. Using V0 for the host, V1 for the first level guest and > V2 for the second level guest, when both V1 and V2 are using nested paging > there are currently a number of unnecessary instruction emulations. When > V2 is launched shadow paging is used in V1 for the nested tables of V2. As > a result, KVM marks these pages as RO in the host nested page tables. When > V2 exits and we resume V1, these pages are still marked RO. > > Every nested walk for a guest page table is treated as a user-level write > access and this causes a lot of NPFs because the V1 page tables are marked > RO in the V0 nested tables. While executing V1, when these NPFs occur KVM > sees a write to a read-only page, emulates the V1 instruction and unprotects > the page (marking it RW). This patch looks for cases where we get a NPF due > to a guest page table walk where the page was marked RO. It immediately > unprotects the page and resumes the guest, leading to far fewer instruction > emulations when nested virtualization is used. > > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx> > --- > arch/x86/include/asm/kvm_host.h | 11 ++++++++++- > arch/x86/kvm/mmu.c | 20 ++++++++++++++++++-- > arch/x86/kvm/svm.c | 2 +- > 3 files changed, 29 insertions(+), 4 deletions(-) FWIW: Reviewed-by: Borislav Petkov <bp@xxxxxxx> -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) -- -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html