backport exposing FLUSHBYASID when running nested VMs on AMD CPUs

[pve-kernel.git] / patches / kernel / 0015-KVM-nSVM-Advertise-support-for-flush-by-ASID.patch

diff --git a/patches/kernel/0015-KVM-nSVM-Advertise-support-for-flush-by-ASID.patch b/patches/kernel/0015-KVM-nSVM-Advertise-support-for-flush-by-ASID.patch
new file mode 100644 (file)
index 0000000..8ae3a67
--- /dev/null
+++ b/patches/kernel/0015-KVM-nSVM-Advertise-support-for-flush-by-ASID.patch
@@ -0,0 +1,39 @@
+From 42af81abf0b96ab661591d024aed55c05dd85b91 Mon Sep 17 00:00:00 2001
+From: Sean Christopherson <seanjc@google.com>
+Date: Wed, 18 Oct 2023 12:41:04 -0700
+Subject: [PATCH 2/2] KVM: nSVM: Advertise support for flush-by-ASID
+
+Advertise support for FLUSHBYASID when nested SVM is enabled, as KVM can
+always emulate flushing TLB entries for a vmcb12 ASID, e.g. by running L2
+with a new, fresh ASID in vmcb02.  Some modern hypervisors, e.g. VMWare
+Workstation 17, require FLUSHBYASID support and will refuse to run if it's
+not present.
+
+Punt on proper support, as "Honor L1's request to flush an ASID on nested
+VMRUN" is one of the TODO items in the (incomplete) list of issues that
+need to be addressed in order for KVM to NOT do a full TLB flush on every
+nested SVM transition (see nested_svm_transition_tlb_flush()).
+
+Reported-by: Stefan Sterz <s.sterz@proxmox.com>
+Closes: https://lkml.kernel.org/r/b9915c9c-4cf6-051a-2d91-44cc6380f455%40proxmox.com
+Signed-off-by: Sean Christopherson <seanjc@google.com>
+Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
+---
+ arch/x86/kvm/svm/svm.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
+index 9a194aa1a75a..0fde9b0c464b 100644
+--- a/arch/x86/kvm/svm/svm.c
++++ b/arch/x86/kvm/svm/svm.c
+@@ -4880,6 +4880,7 @@ static __init void svm_set_cpu_caps(void)
+       if (nested) {
+               kvm_cpu_cap_set(X86_FEATURE_SVM);
+               kvm_cpu_cap_set(X86_FEATURE_VMCBCLEAN);
++              kvm_cpu_cap_set(X86_FEATURE_FLUSHBYASID);
+
+               if (nrips)
+                       kvm_cpu_cap_set(X86_FEATURE_NRIPS);
+--
+2.39.2
+