From: Marc Zyngier <maz@kernel.org>
Date: Mon, 25 Aug 2025 10:24:11 +0000 (+0100)
Subject: KVM: arm64: Don't switch MMU on translation from non-NV context
X-Git-Tag: v6.18-rc1~95^2~5^2~6^2~4
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=61b0280a670bdbb3a209ae474625f387788af0a8;p=thirdparty%2Fkernel%2Flinux.git

KVM: arm64: Don't switch MMU on translation from non-NV context

If calling into the AT code from guest EL1, there is no need
to consider any context switch, as we are guaranteed to be
in the correct context.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index 4efa2167116f..c06a8e831f33 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -1285,7 +1285,7 @@ static u64 __kvm_at_s1e01_fast(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
 {
 	struct mmu_config config;
 	struct kvm_s2_mmu *mmu;
-	bool fail;
+	bool fail, mmu_cs;
 	u64 par;
 
 	par = SYS_PAR_EL1_F;
@@ -1301,8 +1301,13 @@ static u64 __kvm_at_s1e01_fast(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
 	 * If HCR_EL2.{E2H,TGE} == {1,1}, the MMU context is already
 	 * the right one (as we trapped from vEL2). If not, save the
 	 * full MMU context.
+	 *
+	 * We are also guaranteed to be in the correct context if
+	 * we're not in a nested VM.
 	 */
-	if (vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu))
+	mmu_cs = (vcpu_has_nv(vcpu) &&
+		  !(vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu)));
+	if (!mmu_cs)
 		goto skip_mmu_switch;
 
 	/*
@@ -1370,7 +1375,7 @@ skip_mmu_switch:
 
 	write_sysreg_hcr(HCR_HOST_VHE_FLAGS);
 
-	if (!(vcpu_el2_e2h_is_set(vcpu) && vcpu_el2_tge_is_set(vcpu)))
+	if (mmu_cs)
 		__mmu_config_restore(&config);
 
 	return par;