KVM: Let KVM_SET_SIGNAL_MASK work as advertised

KVM API says for the signal mask you set via KVM_SET_SIGNAL_MASK, that
"any unblocked signal received [...] will cause KVM_RUN to return with
-EINTR" and that "the signal will only be delivered if not blocked by
the original signal mask".

This, however, is only true, when the calling task has a signal handler
registered for a signal. If not, signal evaluation is short-circuited for
SIG_IGN and SIG_DFL, and the signal is either ignored without KVM_RUN
returning or the whole process is terminated.

Make KVM_SET_SIGNAL_MASK behave as advertised by utilizing logic similar
to that in do_sigtimedwait() to avoid short-circuiting of signals.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index d535edc..75fdeaa 100644 (file)
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -445,10 +445,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
        int r = -EINTR;
-       sigset_t sigsaved;
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+       kvm_sigset_activate(vcpu);
 
        if (vcpu->mmio_needed) {
                if (!vcpu->mmio_is_write)
@@ -480,8 +478,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
        local_irq_enable();
 
 out:
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+       kvm_sigset_deactivate(vcpu);
 
        return r;
 }

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 6b6c53c..1915e86 100644 (file)
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -1407,7 +1407,6 @@ int kvm_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu, struct kvm_one_reg *reg)
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
        int r;
-       sigset_t sigsaved;
 
        if (vcpu->mmio_needed) {
                vcpu->mmio_needed = 0;
@@ -1448,16 +1447,14 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 #endif
        }
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+       kvm_sigset_activate(vcpu);
 
        if (run->immediate_exit)
                r = -EINTR;
        else
                r = kvmppc_vcpu_run(run, vcpu);
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+       kvm_sigset_deactivate(vcpu);
 
        return r;
 }

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 98ad8b9..9614aea 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3372,7 +3372,6 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
        int rc;
-       sigset_t sigsaved;
 
        if (kvm_run->immediate_exit)
                return -EINTR;
@@ -3382,8 +3381,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                return 0;
        }
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+       kvm_sigset_activate(vcpu);
 
        if (!kvm_s390_user_cpu_state_ctrl(vcpu->kvm)) {
                kvm_s390_vcpu_start(vcpu);
@@ -3417,8 +3415,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
        disable_cpu_timer_accounting(vcpu);
        store_regs(vcpu, kvm_run);
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+       kvm_sigset_deactivate(vcpu);
 
        vcpu->stat.exit_userspace++;
        return rc;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f49fe51..eee8e7f 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7267,12 +7267,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
        struct fpu *fpu = &current->thread.fpu;
        int r;
-       sigset_t sigsaved;
 
        fpu__initialize(fpu);
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+       kvm_sigset_activate(vcpu);
 
        if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
                if (kvm_run->immediate_exit) {
@@ -7315,8 +7313,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
 out:
        post_kvm_run_save(vcpu);
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+       kvm_sigset_deactivate(vcpu);
 
        return r;
 }

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 2e754b7..893d6d6 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -715,6 +715,9 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
                         unsigned long len);
 void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
 
+void kvm_sigset_activate(struct kvm_vcpu *vcpu);
+void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
+
 void kvm_vcpu_block(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);

diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index a6524ff..a67c106 100644 (file)
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -615,7 +615,6 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
        int ret;
-       sigset_t sigsaved;
 
        if (unlikely(!kvm_vcpu_initialized(vcpu)))
                return -ENOEXEC;
@@ -633,8 +632,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
        if (run->immediate_exit)
                return -EINTR;
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
+       kvm_sigset_activate(vcpu);
 
        ret = 1;
        run->exit_reason = KVM_EXIT_UNKNOWN;
@@ -769,8 +767,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
                kvm_pmu_update_run(vcpu);
        }
 
-       if (vcpu->sigset_active)
-               sigprocmask(SIG_SETMASK, &sigsaved, NULL);
+       kvm_sigset_deactivate(vcpu);
+
        return ret;
 }
 

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2dd1a9c..c01cff0 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2065,6 +2065,29 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
+void kvm_sigset_activate(struct kvm_vcpu *vcpu)
+{
+       if (!vcpu->sigset_active)
+               return;
+
+       /*
+        * This does a lockless modification of ->real_blocked, which is fine
+        * because, only current can change ->real_blocked and all readers of
+        * ->real_blocked don't care as long ->real_blocked is always a subset
+        * of ->blocked.
+        */
+       sigprocmask(SIG_SETMASK, &vcpu->sigset, &current->real_blocked);
+}
+
+void kvm_sigset_deactivate(struct kvm_vcpu *vcpu)
+{
+       if (!vcpu->sigset_active)
+               return;
+
+       sigprocmask(SIG_SETMASK, &current->real_blocked, NULL);
+       sigemptyset(&current->real_blocked);
+}
+
 static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
        unsigned int old, val, grow;