KVM: arm64: Commit pending PC adjustemnts before returning to userspace

KVM currently updates PC (and the corresponding exception state)
using a two phase approach: first by setting a set of flags,
then by converting these flags into a state update when the vcpu
is about to enter the guest.

However, this creates a disconnect with userspace if the vcpu thread
returns there with any exception/PC flag set. In this case, the exposed
context is wrong, as userspace doesn't have access to these flags
(they aren't architectural). It also means that these flags are
preserved across a reset, which isn't expected.

To solve this problem, force an explicit synchronisation of the
exception state on vcpu exit to userspace. As an optimisation
for nVHE systems, only perform this when there is something pending.

Reported-by: Zenghui Yu <yuzenghui@huawei.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Tested-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org # 5.11

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index d5b1103..5e9b33c 100644 (file)
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -63,6 +63,7 @@
 #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector            18
 #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize             19
 #define __KVM_HOST_SMCCC_FUNC___pkvm_mark_hyp                  20
+#define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc                  21
 
 #ifndef __ASSEMBLY__
 

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 1cb39c0..1126eae 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -897,6 +897,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
        kvm_sigset_deactivate(vcpu);
 
+       /*
+        * In the unlikely event that we are returning to userspace
+        * with pending exceptions or PC adjustment, commit these
+        * adjustments in order to give userspace a consistent view of
+        * the vcpu state. Note that this relies on __kvm_adjust_pc()
+        * being preempt-safe on VHE.
+        */
+       if (unlikely(vcpu->arch.flags & (KVM_ARM64_PENDING_EXCEPTION |
+                                        KVM_ARM64_INCREMENT_PC)))
+               kvm_call_hyp(__kvm_adjust_pc, vcpu);
+
        vcpu_put(vcpu);
        return ret;
 }

diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c
index 0812a49..11541b9 100644 (file)
--- a/arch/arm64/kvm/hyp/exception.c
+++ b/arch/arm64/kvm/hyp/exception.c
@@ -331,8 +331,8 @@ static void kvm_inject_exception(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Adjust the guest PC on entry, depending on flags provided by EL1
- * for the purpose of emulation (MMIO, sysreg) or exception injection.
+ * Adjust the guest PC (and potentially exception state) depending on
+ * flags provided by the emulation code.
  */
 void __kvm_adjust_pc(struct kvm_vcpu *vcpu)
 {

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index f36420a..1632f00 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -28,6 +28,13 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
        cpu_reg(host_ctxt, 1) =  __kvm_vcpu_run(kern_hyp_va(vcpu));
 }
 
+static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt)
+{
+       DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1);
+
+       __kvm_adjust_pc(kern_hyp_va(vcpu));
+}
+
 static void handle___kvm_flush_vm_context(struct kvm_cpu_context *host_ctxt)
 {
        __kvm_flush_vm_context();
@@ -170,6 +177,7 @@ typedef void (*hcall_t)(struct kvm_cpu_context *);
 
 static const hcall_t host_hcall[] = {
        HANDLE_FUNC(__kvm_vcpu_run),
+       HANDLE_FUNC(__kvm_adjust_pc),
        HANDLE_FUNC(__kvm_flush_vm_context),
        HANDLE_FUNC(__kvm_tlb_flush_vmid_ipa),
        HANDLE_FUNC(__kvm_tlb_flush_vmid),