[PATCH v2 16/18] KVM: arm64: Introduce __pkvm_tlb_flush_vmid()

[Quentin Perret <qperret@google.com>]

Introduce a new hypercall to flush the TLBs of non-protected guests. The
host kernel will be responsible for issuing this hypercall after changing
stage-2 permissions using the __pkvm_host_relax_guest_perms() or
__pkvm_host_wrprotect_guest() paths. This is left under the host's
responsibility for performance reasons.

Note however that the TLB maintenance for all *unmap* operations still
remains entirely under the hypervisor's responsibility for security
reasons -- an unmapped page may be donated to another entity, so a stale
TLB entry could be used to leak private data.

Signed-off-by: Quentin Perret <qperret@google.com>
---
 arch/arm64/include/asm/kvm_asm.h   |  1 +
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 6178e12a0dbc..df6237d0459c 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -87,6 +87,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_teardown_vm,
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
 	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
+	__KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index de0012a75827..219d7fb850ec 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -398,6 +398,22 @@ static void handle___kvm_tlb_flush_vmid(struct kvm_cpu_context *host_ctxt)
 	__kvm_tlb_flush_vmid(kern_hyp_va(mmu));
 }
 
+static void handle___pkvm_tlb_flush_vmid(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
+	struct pkvm_hyp_vm *hyp_vm;
+
+	if (!is_protected_kvm_enabled())
+		return;
+
+	hyp_vm = get_pkvm_hyp_vm(handle);
+	if (!hyp_vm)
+		return;
+
+	__kvm_tlb_flush_vmid(&hyp_vm->kvm.arch.mmu);
+	put_pkvm_hyp_vm(hyp_vm);
+}
+
 static void handle___kvm_flush_cpu_context(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(struct kvm_s2_mmu *, mmu, host_ctxt, 1);
@@ -582,6 +598,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_teardown_vm),
 	HANDLE_FUNC(__pkvm_vcpu_load),
 	HANDLE_FUNC(__pkvm_vcpu_put),
+	HANDLE_FUNC(__pkvm_tlb_flush_vmid),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
-- 
2.47.0.338.g60cca15819-goog