FAILED: patch "[PATCH] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 112022bdb5bc372e00e6e43cb88ee38ea67b97bd Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Tue, 22 Jun 2021 10:56:47 -0700
Subject: [PATCH] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP
shadow MMUs

Mark NX as being used for all non-nested shadow MMUs, as KVM will set the NX bit for huge SPTEs if the iTLB mutli-hit mitigation is enabled. Checking the mitigation itself is not sufficient as it can be toggled on at any time and KVM doesn't reset MMU contexts when that happens. KVM could reset the contexts, but that would require purging all SPTEs in all MMUs, for no real benefit. And, KVM already forces EFER.NX=1 when TDP is disabled (for WP=0, SMEP=1, NX=0), so technically NX is never reserved for shadow MMUs.

Message-Id: <[email protected]>

index b3be690d081a..444e068e6ad9 100644
@@ -4221,7 +4221,15 @@ static inline u64 reserved_hpa_bits(void)
 void
 reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
 {
-	bool uses_nx = context->nx ||
+	/*
+	 * KVM uses NX when TDP is disabled to handle a variety of scenarios,
+	 * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
+	 * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
+	 * The iTLB multi-hit workaround can be toggled at any time, so assume
+	 * NX can be used by any non-nested shadow MMU to avoid having to reset
+	 * MMU contexts.  Note, KVM forces EFER.NX=1 when TDP is disabled.
+	 */
+	bool uses_nx = context->nx || !tdp_enabled ||
 		context->mmu_role.base.smep_andnot_wp;
 	struct rsvd_bits_validate *shadow_zero_check;
 	int i;

Hi Greg,

Here is the backport, will also apply to 4.14-stable.

--
Regards
Sudip

From 19073fb2fa74d528620a0f0a1e2bf442c14a67ec Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Tue, 22 Jun 2021 10:56:47 -0700
Subject: [PATCH] KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP
shadow MMUs

commit 112022bdb5bc372e00e6e43cb88ee38ea67b97bd upstream

Mark NX as being used for all non-nested shadow MMUs, as KVM will set the NX bit for huge SPTEs if the iTLB mutli-hit mitigation is enabled. Checking the mitigation itself is not sufficient as it can be toggled on at any time and KVM doesn't reset MMU contexts when that happens. KVM could reset the contexts, but that would require purging all SPTEs in all MMUs, for no real benefit. And, KVM already forces EFER.NX=1 when TDP is disabled (for WP=0, SMEP=1, NX=0), so technically NX is never reserved for shadow MMUs.

Message-Id: <[email protected]>

---
 arch/x86/kvm/mmu.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

index 762baba4ecd5..0cb82172c06c 100644
@@ -4557,7 +4557,16 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu,
 void
 reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
 {
-	bool uses_nx = context->nx || context->base_role.smep_andnot_wp;
+	/*
+	 * KVM uses NX when TDP is disabled to handle a variety of scenarios,
+	 * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and
+	 * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0.
+	 * The iTLB multi-hit workaround can be toggled at any time, so assume
+	 * NX can be used by any non-nested shadow MMU to avoid having to reset
+	 * MMU contexts.  Note, KVM forces EFER.NX=1 when TDP is disabled.
+	 */
+	bool uses_nx = context->nx || !tdp_enabled ||
+		context->base_role.smep_andnot_wp;
 	struct rsvd_bits_validate *shadow_zero_check;
 	int i;
 

2.30.2