Messages in this thread Patch in this message | | | From | "Kalra, Ashish" <> | Subject | RE: [PATCH Part2 v5 27/45] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command | Date | Wed, 18 May 2022 20:35:51 +0000 |
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[AMD Official Use Only - General]
Hello Marc,
-----Original Message----- From: Marc Orr <marcorr@google.com> Sent: Wednesday, May 18, 2022 3:21 PM To: Kalra, Ashish <Ashish.Kalra@amd.com> Cc: x86 <x86@kernel.org>; LKML <linux-kernel@vger.kernel.org>; kvm list <kvm@vger.kernel.org>; linux-coco@lists.linux.dev; linux-mm@kvack.org; Linux Crypto Mailing List <linux-crypto@vger.kernel.org>; Thomas Gleixner <tglx@linutronix.de>; Ingo Molnar <mingo@redhat.com>; Joerg Roedel <jroedel@suse.de>; Lendacky, Thomas <Thomas.Lendacky@amd.com>; H. Peter Anvin <hpa@zytor.com>; Ard Biesheuvel <ardb@kernel.org>; Paolo Bonzini <pbonzini@redhat.com>; Sean Christopherson <seanjc@google.com>; Vitaly Kuznetsov <vkuznets@redhat.com>; Wanpeng Li <wanpengli@tencent.com>; Jim Mattson <jmattson@google.com>; Andy Lutomirski <luto@kernel.org>; Dave Hansen <dave.hansen@linux.intel.com>; Sergio Lopez <slp@redhat.com>; Peter Gonda <pgonda@google.com>; Peter Zijlstra <peterz@infradead.org>; Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>; David Rientjes <rientjes@google.com>; Dov Murik <dovmurik@linux.ibm.com>; Tobin Feldman-Fitzthum <tobin@ibm.com>; Borislav Petkov <bp@alien8.de>; Roth, Michael <Michael.Roth@amd.com>; Vlastimil Babka <vbabka@suse.cz>; Kirill A . Shutemov <kirill@shutemov.name>; Andi Kleen <ak@linux.intel.com>; Tony Luck <tony.luck@intel.com>; Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>; Alper Gun <alpergun@google.com> Subject: Re: [PATCH Part2 v5 27/45] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command
> @@ -2364,16 +2467,29 @@ static void sev_flush_guest_memory(struct > vcpu_svm *svm, void *va, void sev_free_vcpu(struct kvm_vcpu *vcpu) { > struct vcpu_svm *svm; > + u64 pfn; > > if (!sev_es_guest(vcpu->kvm)) > return; > > svm = to_svm(vcpu); > + pfn = __pa(svm->vmsa) >> PAGE_SHIFT; > > if (vcpu->arch.guest_state_protected) > sev_flush_guest_memory(svm, svm->vmsa, PAGE_SIZE); > + > + /* > + * If its an SNP guest, then VMSA was added in the RMP entry as > + * a guest owned page. Transition the page to hyperivosr state > + * before releasing it back to the system. > + */ > + if (sev_snp_guest(vcpu->kvm) && > + host_rmp_make_shared(pfn, PG_LEVEL_4K, false)) > + goto skip_vmsa_free; > + > __free_page(virt_to_page(svm->vmsa)); > > +skip_vmsa_free: > if (svm->ghcb_sa_free) > kfree(svm->ghcb_sa); > }
>Hi Ashish. We're still working with this patch set internally. We found a bug that I wanted to report in this patch. Above, we need to flush the VMSA page, `svm->vmsa`, _after_ we call `host_rmp_make_shared()` to mark the page is shared. >Otherwise, the host gets an RMP violation when it tries to flush the guest-owned VMSA page.
>The bug was silent, at least on our Milan platforms, bef reo >d45829b351ee6 ("KVM: SVM: Flush when freeing encrypted pages even on SME_COHERENT CPUs"), because the `sev_flush_guest_memory()` helper was a noop on platforms with the SME_COHERENT feature. However, after d45829b351ee6, we >unconditionally do the flush to keep the IO address space coherent. And then we hit this bug.
Yes I have already hit this bug and added a fix as below:
commit 944fba38cbd3baf1ece76197630bd45e83089f14 Author: Ashish Kalra <ashish.kalra@amd.com> Date: Tue May 3 14:33:29 2022 +0000
KVM: SVM: Fix VMSA flush for an SNP guest. If its an SNP guest, then VMSA was added in the RMP entry as a guest owned page and also removed from the kernel direct map so flush it later after it is transitioned back to hypervisor state and restored in the direct map. Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index cc7c34d8b0db..0f772a0f1d35 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2840,27 +2840,23 @@ void sev_free_vcpu(struct kvm_vcpu *vcpu) svm = to_svm(vcpu); - if (vcpu->arch.guest_state_protected) - sev_flush_encrypted_page(vcpu, svm->sev_es.vmsa); - /* * If its an SNP guest, then VMSA was added in the RMP entry as * a guest owned page. Transition the page to hyperivosr state * before releasing it back to the system. + * Also the page is removed from the kernel direct map, so flush it + * later after it is transitioned back to hypervisor state and + * restored in the direct map. */ if (sev_snp_guest(vcpu->kvm)) { u64 pfn = __pa(svm->sev_es.vmsa) >> PAGE_SHIFT; if (host_rmp_make_shared(pfn, PG_LEVEL_4K, false)) goto skip_vmsa_free; } + if (vcpu->arch.guest_state_protected) + sev_flush_encrypted_page(vcpu, svm->sev_es.vmsa); + __free_page(virt_to_page(svm->sev_es.vmsa)); skip_vmsa_free:
This will be part of the next hypervisor patches which we will be posting next. Thanks, Ashish
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