From e7dda8ec9fc9020e4f53345cdbb18a2e82e54a65 Mon Sep 17 00:00:00 2001 From: Dongxiao Xu Date: Wed, 30 Jan 2013 09:17:30 -0800 Subject: [PATCH] VMX: disable SMEP feature when guest is in non-paging mode SMEP is disabled if CPU is in non-paging mode in hardware. However Xen always uses paging mode to emulate guest non-paging mode with HAP. To emulate this behavior, SMEP needs to be manually disabled when guest switches to non-paging mode. We met an issue that, SMP Linux guest with recent kernel (enable SMEP support, for example, 3.5.3) would crash with triple fault if setting unrestricted_guest=0 in grub. This is because Xen uses an identity mapping page table to emulate the non-paging mode, where the page table is set with USER flag. If SMEP is still enabled in this case, guest will meet unhandlable page fault and then crash. Signed-off-by: Dongxiao Xu Signed-off-by: Xiantao Zhang Committed-by: Keir Fraser --- xen/arch/x86/hvm/vmx/vmx.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index 99731927c7..e623c915e6 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -1162,6 +1162,13 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr) { v->arch.hvm_vcpu.hw_cr[4] |= X86_CR4_PSE; v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_PAE; + /* + * SMEP is disabled if CPU is in non-paging mode in hardware. + * However Xen always uses paging mode to emulate guest non-paging + * mode with HAP. To emulate this behavior, SMEP needs to be + * manually disabled when guest switches to non-paging mode. + */ + v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_SMEP; } __vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]); __vmwrite(CR4_READ_SHADOW, v->arch.hvm_vcpu.guest_cr[4]); -- 2.30.2