Commit 9078210e authored Oct 25, 2016 by James Hogan Committed by Paolo Bonzini Oct 26, 2016

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: 25b08c7f ("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>

parent 07d9a380

arch/mips/kvm/mips.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}
		}

arch/mips/kvm/mmu.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -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,

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