KVM: MIPS: Fix lazy user ASID regenerate for SMP

kvm_mips_check_asids() runs before entering the guest and performs lazy
regeneration of host ASID for guest usermode, using last_user_gasid to
track the last guest ASID in the VCPU that was used by guest usermode on
any host CPU.

last_user_gasid is reset after performing the lazy ASID regeneration on
the current CPU, and by kvm_arch_vcpu_load() if the host ASID for guest
usermode is regenerated due to staleness (to cancel outstanding lazy
ASID regenerations). Unfortunately neither case handles SMP hosts
correctly:

 - When the lazy ASID regeneration is performed it should apply to all
   CPUs (as last_user_gasid does), so reset the ASID on other CPUs to
   zero to trigger regeneration when the VCPU is next loaded on those
   CPUs.

 - When the ASID is found to be stale on the current CPU, we should not
   cancel lazy ASID regenerations globally, so drop the reset of
   last_user_gasid altogether here.

Both cases would require a guest ASID change and two host CPU migrations
(and in the latter case one of the CPUs to start a new ASID cycle)
before guest usermode could potentially access stale user pages from a
previously running ASID in the same VCPU.

Fixes: 25b08c7fb0e4 ("KVM: MIPS: Invalidate TLB by regenerating ASIDs")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 4 insertions, 5 deletions

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 622037d851a3..06a60b19acfb 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -426,7 +426,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 static void kvm_mips_check_asids(struct kvm_vcpu *vcpu)
 {
         struct mips_coproc *cop0 = vcpu->arch.cop0;
-        int cpu = smp_processor_id();
+        int i, cpu = smp_processor_id();
         unsigned int gasid;
 
         /*
@@ -442,6 +442,9 @@ static void kvm_mips_check_asids(struct kvm_vcpu *vcpu)
                                                 vcpu);
                         vcpu->arch.guest_user_asid[cpu] =
                                 vcpu->arch.guest_user_mm.context.asid[cpu];
+                        for_each_possible_cpu(i)
+                                if (i != cpu)
+                                        vcpu->arch.guest_user_asid[cpu] = 0;
                         vcpu->arch.last_user_gasid = gasid;
                 }
         }
diff --git a/arch/mips/kvm/mmu.c b/arch/mips/kvm/mmu.c
index 03883ba806e2..3b677c851be0 100644
--- a/arch/mips/kvm/mmu.c
+++ b/arch/mips/kvm/mmu.c
@@ -260,13 +260,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
         if ((vcpu->arch.guest_user_asid[cpu] ^ asid_cache(cpu)) &
                                                 asid_version_mask(cpu)) {
-                u32 gasid = kvm_read_c0_guest_entryhi(vcpu->arch.cop0) &
-                                KVM_ENTRYHI_ASID;
-
                 kvm_get_new_mmu_context(&vcpu->arch.guest_user_mm, cpu, vcpu);
                 vcpu->arch.guest_user_asid[cpu] =
                     vcpu->arch.guest_user_mm.context.asid[cpu];
-                vcpu->arch.last_user_gasid = gasid;
                 newasid++;
 
                 kvm_debug("[%d]: cpu_context: %#lx\n", cpu,