KVM: arm64: Support TLB invalidation in guest context

Typically, TLB invalidation of guest stage-2 mappings using nVHE is
performed by a hypercall originating from the host. For the invalidation
instruction to be effective, therefore, __tlb_switch_to_{guest,host}()
swizzle the active stage-2 context around the TLBI instruction.

With guest-to-host memory sharing and unsharing hypercalls
originating from the guest under pKVM, there is need to support
both guest and host VMID invalidations issued from guest context.

Replace the __tlb_switch_to_{guest,host}() functions with a more general
{enter,exit}_vmid_context() implementation which supports being invoked
from guest context and acts as a no-op if the target context matches the
running context.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-10-tabba@google.comSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/hyp/nvhe/tlb.c

@@ -11,13 +11,23 @@
 #include <nvhe/mem_protect.h>
 
 struct tlb_inv_context {
+	struct kvm_s2_mmu	*mmu;
 	u64			tcr;
+	u64			sctlr;
 };
 
-static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
+static void enter_vmid_context(struct kvm_s2_mmu *mmu,
 			       struct tlb_inv_context *cxt,
 			       bool nsh)
 {
+	struct kvm_s2_mmu *host_s2_mmu = &host_mmu.arch.mmu;
+	struct kvm_cpu_context *host_ctxt;
+	struct kvm_vcpu *vcpu;
+
+	host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
+	vcpu = host_ctxt->__hyp_running_vcpu;
+	cxt->mmu = NULL;
+
 	/*
 	 * We have two requirements:
 	 *
@@ -40,20 +50,55 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
 	else
 		dsb(ish);
 
+	/*
+	 * If we're already in the desired context, then there's nothing to do.
+	 */
+	if (vcpu) {
+		/*
+		 * We're in guest context. However, for this to work, this needs
+		 * to be called from within __kvm_vcpu_run(), which ensures that
+		 * __hyp_running_vcpu is set to the current guest vcpu.
+		 */
+		if (mmu == vcpu->arch.hw_mmu || WARN_ON(mmu != host_s2_mmu))
+			return;
+
+		cxt->mmu = vcpu->arch.hw_mmu;
+	} else {
+		/* We're in host context. */
+		if (mmu == host_s2_mmu)
+			return;
+
+		cxt->mmu = host_s2_mmu;
+	}
+
 	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
 		u64 val;
 
 		/*
 		 * For CPUs that are affected by ARM 1319367, we need to
-		 * avoid a host Stage-1 walk while we have the guest's
-		 * VMID set in the VTTBR in order to invalidate TLBs.
-		 * We're guaranteed that the S1 MMU is enabled, so we can
-		 * simply set the EPD bits to avoid any further TLB fill.
+		 * avoid a Stage-1 walk with the old VMID while we have
+		 * the new VMID set in the VTTBR in order to invalidate TLBs.
+		 * We're guaranteed that the host S1 MMU is enabled, so
+		 * we can simply set the EPD bits to avoid any further
+		 * TLB fill. For guests, we ensure that the S1 MMU is
+		 * temporarily enabled in the next context.
 		 */
 		val = cxt->tcr = read_sysreg_el1(SYS_TCR);
 		val |= TCR_EPD1_MASK | TCR_EPD0_MASK;
 		write_sysreg_el1(val, SYS_TCR);
 		isb();
+
+		if (vcpu) {
+			val = cxt->sctlr = read_sysreg_el1(SYS_SCTLR);
+			if (!(val & SCTLR_ELx_M)) {
+				val |= SCTLR_ELx_M;
+				write_sysreg_el1(val, SYS_SCTLR);
+				isb();
+			}
+		} else {
+			/* The host S1 MMU is always enabled. */
+			cxt->sctlr = SCTLR_ELx_M;
+		}
 	}
 
 	/*
@@ -62,18 +107,40 @@ static void __tlb_switch_to_guest(struct kvm_s2_mmu *mmu,
 	 * ensuring that we always have an ISB, but not two ISBs back
 	 * to back.
 	 */
+	if (vcpu)
+		__load_host_stage2();
+	else
 		__load_stage2(mmu, kern_hyp_va(mmu->arch));
+
 	asm(ALTERNATIVE("isb", "nop", ARM64_WORKAROUND_SPECULATIVE_AT));
 }
 
-static void __tlb_switch_to_host(struct tlb_inv_context *cxt)
+static void exit_vmid_context(struct tlb_inv_context *cxt)
 {
+	struct kvm_s2_mmu *mmu = cxt->mmu;
+	struct kvm_cpu_context *host_ctxt;
+	struct kvm_vcpu *vcpu;
+
+	host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
+	vcpu = host_ctxt->__hyp_running_vcpu;
+
+	if (!mmu)
+		return;
+
+	if (vcpu)
+		__load_stage2(mmu, kern_hyp_va(mmu->arch));
+	else
 		__load_host_stage2();
 
 	if (cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT)) {
-		/* Ensure write of the host VMID */
+		/* Ensure write of the old VMID */
+		isb();
+
+		if (!(cxt->sctlr & SCTLR_ELx_M)) {
+			write_sysreg_el1(cxt->sctlr, SYS_SCTLR);
 			isb();
-		/* Restore the host's TCR_EL1 */
+		}
+
 		write_sysreg_el1(cxt->tcr, SYS_TCR);
 	}
 }
@@ -84,7 +151,7 @@ void __kvm_tlb_flush_vmid_ipa(struct kvm_s2_mmu *mmu,
 	struct tlb_inv_context cxt;
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt, false);
+	enter_vmid_context(mmu, &cxt, false);
 
 	/*
 	 * We could do so much better if we had the VA as well.
@@ -105,7 +172,7 @@ void __kvm_tlb_flush_vmid_ipa(struct kvm_s2_mmu *mmu,
 	dsb(ish);
 	isb();
 
-	__tlb_switch_to_host(&cxt);
+	exit_vmid_context(&cxt);
 }
 
 void __kvm_tlb_flush_vmid_ipa_nsh(struct kvm_s2_mmu *mmu,
@@ -114,7 +181,7 @@ void __kvm_tlb_flush_vmid_ipa_nsh(struct kvm_s2_mmu *mmu,
 	struct tlb_inv_context cxt;
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt, true);
+	enter_vmid_context(mmu, &cxt, true);
 
 	/*
 	 * We could do so much better if we had the VA as well.
@@ -135,7 +202,7 @@ void __kvm_tlb_flush_vmid_ipa_nsh(struct kvm_s2_mmu *mmu,
 	dsb(nsh);
 	isb();
 
-	__tlb_switch_to_host(&cxt);
+	exit_vmid_context(&cxt);
 }
 
 void __kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
@@ -152,7 +219,7 @@ void __kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
 	start = round_down(start, stride);
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt, false);
+	enter_vmid_context(mmu, &cxt, false);
 
 	__flush_s2_tlb_range_op(ipas2e1is, start, pages, stride, 0);
 
@@ -161,7 +228,7 @@ void __kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
 	dsb(ish);
 	isb();
 
-	__tlb_switch_to_host(&cxt);
+	exit_vmid_context(&cxt);
 }
 
 void __kvm_tlb_flush_vmid(struct kvm_s2_mmu *mmu)
@@ -169,13 +236,13 @@ void __kvm_tlb_flush_vmid(struct kvm_s2_mmu *mmu)
 	struct tlb_inv_context cxt;
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt, false);
+	enter_vmid_context(mmu, &cxt, false);
 
 	__tlbi(vmalls12e1is);
 	dsb(ish);
 	isb();
 
-	__tlb_switch_to_host(&cxt);
+	exit_vmid_context(&cxt);
 }
 
 void __kvm_flush_cpu_context(struct kvm_s2_mmu *mmu)
@@ -183,19 +250,19 @@ void __kvm_flush_cpu_context(struct kvm_s2_mmu *mmu)
 	struct tlb_inv_context cxt;
 
 	/* Switch to requested VMID */
-	__tlb_switch_to_guest(mmu, &cxt, false);
+	enter_vmid_context(mmu, &cxt, false);
 
 	__tlbi(vmalle1);
 	asm volatile("ic iallu");
 	dsb(nsh);
 	isb();
 
-	__tlb_switch_to_host(&cxt);
+	exit_vmid_context(&cxt);
 }
 
 void __kvm_flush_vm_context(void)
 {
-	/* Same remark as in __tlb_switch_to_guest() */
+	/* Same remark as in enter_vmid_context() */
 	dsb(ish);
 	__tlbi(alle1is);
 	dsb(ish);