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+From 08d71587b34c95d5461a6bdd946dc1dd46888bf3 Mon Sep 17 00:00:00 2001
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+From: Paolo Bonzini <[email protected]>
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+Date: Thu, 26 Oct 2017 09:13:27 +0200
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+Subject: [PATCH 10/10] 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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+
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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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+
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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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+
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+Thanks a lot to [email protected] 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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+
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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: [email protected]
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+Signed-off-by: Paolo Bonzini <[email protected]>
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+Reviewed-by: David Hildenbrand <[email protected]>
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+Tested-by: Nick Sarnie <[email protected]>
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+Signed-off-by: Radim Krčmář <[email protected]>
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+(cherry picked from commit 15038e14724799b8c205beb5f20f9e54896013c3)
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+Signed-off-by: Fabian Grünbichler <[email protected]>
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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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+
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+diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
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+index af256b786a70..af09baa3d736 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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+@@ -3626,6 +3626,13 @@ 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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+
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