a70918fbbc
rebase on Ubuntu-4.13.0-32.35 the effective kernel tree which gets compiled after patches have been applied is functionally identical (modulo parts for architectures which we don't care about and Ubuntu build files)
57 lines
2.0 KiB
Diff
57 lines
2.0 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Thu, 26 Oct 2017 09:13:27 +0200
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Subject: [PATCH] KVM: SVM: obey guest PAT
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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For many years some users of assigned devices have reported worse
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performance on AMD processors with NPT than on AMD without NPT,
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Intel or bare metal.
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The reason turned out to be that SVM is discarding the guest PAT
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setting and uses the default (PA0=PA4=WB, PA1=PA5=WT, PA2=PA6=UC-,
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PA3=UC). The guest might be using a different setting, and
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especially might want write combining but isn't getting it
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(instead getting slow UC or UC- accesses).
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Thanks a lot to geoff@hostfission.com for noticing the relation
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to the g_pat setting. The patch has been tested also by a bunch
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of people on VFIO users forums.
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Fixes: 709ddebf81cb40e3c36c6109a7892e8b93a09464
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Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196409
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Cc: stable@vger.kernel.org
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Reviewed-by: David Hildenbrand <david@redhat.com>
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Tested-by: Nick Sarnie <commendsarnex@gmail.com>
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Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
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(cherry picked from commit 15038e14724799b8c205beb5f20f9e54896013c3)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/kvm/svm.c | 7 +++++++
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1 file changed, 7 insertions(+)
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diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
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index 55fb408465f7..e99bdfcc6b01 100644
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--- a/arch/x86/kvm/svm.c
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+++ b/arch/x86/kvm/svm.c
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@@ -3649,6 +3649,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
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u32 ecx = msr->index;
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u64 data = msr->data;
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switch (ecx) {
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+ case MSR_IA32_CR_PAT:
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+ if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
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+ return 1;
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+ vcpu->arch.pat = data;
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+ svm->vmcb->save.g_pat = data;
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+ mark_dirty(svm->vmcb, VMCB_NPT);
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+ break;
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case MSR_IA32_TSC:
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kvm_write_tsc(vcpu, msr);
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break;
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--
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2.14.2
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