From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH] kvm: svm: reset mmu on VCPU reset Date: Mon, 21 Sep 2015 10:14:56 +0800 Message-ID: <55FF6820.5040406@linux.intel.com> References: <1442583545-266967-1-git-send-email-imammedo@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: joro@8bytes.org, pbonzini@redhat.com, kvm@vger.kernel.org To: Igor Mammedov , linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1442583545-266967-1-git-send-email-imammedo@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 09/18/2015 09:39 PM, Igor Mammedov wrote: > When INIT/SIPI sequence is sent to VCPU which before that > was in use by OS, VMRUN might fail with: > > KVM: entry failed, hardware error 0xffffffff > EAX=3D00000000 EBX=3D00000000 ECX=3D00000000 EDX=3D000006d3 > ESI=3D00000000 EDI=3D00000000 EBP=3D00000000 ESP=3D00000000 > EIP=3D00000000 EFL=3D00000002 [-------] CPL=3D0 II=3D0 A20=3D1 SMM=3D= 0 HLT=3D0 > ES =3D0000 00000000 0000ffff 00009300 > CS =3D9a00 0009a000 0000ffff 00009a00 > [...] > CR0=3D60000010 CR2=3Db6f3e000 CR3=3D01942000 CR4=3D000007e0 > [...] > EFER=3D0000000000000000 > > with corresponding SVM error: > KVM: FAILED VMRUN WITH VMCB: > [...] > cpl: 0 efer: 0000000000001000 > cr0: 0000000080010010 cr2: 00007fd7fe85bf90 > cr3: 0000000187d0c000 cr4: 0000000000000020 > [...] > > What happens is that VCPU state right after offlinig: > CR0: 0x80050033 EFER: 0xd01 CR4: 0x7e0 > -> long mode with CR3 pointing to longmode page tables > > and when VCPU gets INIT/SIPI following transition happens > CR0: 0 -> 0x60000010 EFER: 0x0 CR4: 0x7e0 > -> paging disabled with stale CR3 > > However SVM under the hood puts VCPU in Paged Real Mode* > which effectively translates CR0 0x60000010 -> 80010010 after > > svm_vcpu_reset() > -> init_vmcb() > -> kvm_set_cr0() > -> svm_set_cr0() > > but from kvm_set_cr0() perspective CR0: 0 -> 0x60000010 > only caching bits are changed and > commit d81135a57aa6 > ("KVM: x86: do not reset mmu if CR0.CD and CR0.NW are changed")' > regressed svm_vcpu_reset() which relied on MMU being reset. > > As result VMRUN after svm_vcpu_reset() tries to run > VCPU in Paged Real Mode with stale MMU context (longmode page tables)= , > which causes some AMD CPUs** to bail out with VMEXIT_INVALID. > > Fix issue by unconditionally resetting MMU context > at init_vmcb() time. > > -- > * AMD64 Architecture Programmer=E2=80=99s Manual, > Volume 2: System Programming, rev: 3.25 > 15.19 Paged Real Mode > ** Opteron 1216 > Good catch and nice analysis. Thanks for your fix, Igor! Reviewed-by: Xiao Guangrong