pve-edge-kernel/patches/kernel/0014-KVM-SVM-obey-guest-PAT.patch

From a0212ec7cc4bc2f88c4435cca881d21f2b079a80 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <[email protected]>
Date: Thu, 26 Oct 2017 09:13:27 +0200
Subject: [PATCH 014/242] KVM: SVM: obey guest PAT
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For many years some users of assigned devices have reported worse
performance on AMD processors with NPT than on AMD without NPT,
Intel or bare metal.

The reason turned out to be that SVM is discarding the guest PAT
setting and uses the default (PA0=PA4=WB, PA1=PA5=WT, PA2=PA6=UC-,
PA3=UC).  The guest might be using a different setting, and
especially might want write combining but isn't getting it
(instead getting slow UC or UC- accesses).

Thanks a lot to [email protected] for noticing the relation
to the g_pat setting.  The patch has been tested also by a bunch
of people on VFIO users forums.

Fixes: 709ddebf81cb40e3c36c6109a7892e8b93a09464
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196409
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Tested-by: Nick Sarnie <[email protected]>
Signed-off-by: Radim Krčmář <[email protected]>
(cherry picked from commit 15038e14724799b8c205beb5f20f9e54896013c3)
Signed-off-by: Fabian Grünbichler <[email protected]>
---
 arch/x86/kvm/svm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index af256b786a70..af09baa3d736 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3626,6 +3626,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 	u32 ecx = msr->index;
 	u64 data = msr->data;
 	switch (ecx) {
+	case MSR_IA32_CR_PAT:
+		if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
+			return 1;
+		vcpu->arch.pat = data;
+		svm->vmcb->save.g_pat = data;
+		mark_dirty(svm->vmcb, VMCB_NPT);
+		break;
 	case MSR_IA32_TSC:
 		kvm_write_tsc(vcpu, msr);
 		break;
-- 
2.14.2