On Fri, Dec 09, 2022 at 09:03:45PM +0000, Sean Christopherson wrote:
[...]
- GUEST_ASSERT(0);
+out:
- /*
* If the guest cannot grab a ucall structure from the pool then the* only option to get out to userspace is a bare ucall. This is probably* a good time to mention that guest assertions depend on ucalls with* arguments too.*/- GUEST_UCALL_NONE();
UCALL_NONE isn't much better than infinite stack recursion, e.g. a test might end up passing by dumb luck, or go in the wrong direction because it sometimes handles UCALL_NONE.
Oh, I was just seeking an end to my misery. Yeah, we can use a magic value to signal this instead.
How about this?
LGTM.
-- Thanks, Oliver
From: Sean Christopherson seanjc@google.com Date: Fri, 9 Dec 2022 12:55:44 -0800 Subject: [PATCH] KVM: selftests: Use magic value to signal ucall_alloc() failure
Use a magic value to signal a ucall_alloc() failure instead of simply doing GUEST_ASSERT(). GUEST_ASSERT() relies on ucall_alloc() and so a failure puts the guest into an infinite loop.
Use -1 as the magic value, as a real ucall struct should never wrap.
Reported-by: Oliver Upton oliver.upton@linux.dev Signed-off-by: Sean Christopherson seanjc@google.com
tools/testing/selftests/kvm/lib/ucall_common.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c index 0cc0971ce60e..2f0e2ea941cc 100644 --- a/tools/testing/selftests/kvm/lib/ucall_common.c +++ b/tools/testing/selftests/kvm/lib/ucall_common.c @@ -4,6 +4,8 @@ #include "linux/bitmap.h" #include "linux/atomic.h" +#define GUEST_UCALL_FAILED -1
struct ucall_header { DECLARE_BITMAP(in_use, KVM_MAX_VCPUS); struct ucall ucalls[KVM_MAX_VCPUS]; @@ -41,7 +43,8 @@ static struct ucall *ucall_alloc(void) struct ucall *uc; int i;
- GUEST_ASSERT(ucall_pool);
- if (!ucall_pool)
goto ucall_failed;for (i = 0; i < KVM_MAX_VCPUS; ++i) { if (!test_and_set_bit(i, ucall_pool->in_use)) { @@ -51,7 +54,13 @@ static struct ucall *ucall_alloc(void) } }
- GUEST_ASSERT(0);
+ucall_failed:
- /*
* If the vCPU cannot grab a ucall structure, make a bare ucall with a* magic value to signal to get_ucall() that things went sideways.* GUEST_ASSERT() depends on ucall_alloc() and so cannot be used here.*/- ucall_arch_do_ucall(GUEST_UCALL_FAILED); return NULL;
} @@ -93,6 +102,9 @@ uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc) addr = ucall_arch_get_ucall(vcpu); if (addr) {
TEST_ASSERT(addr != (void *)GUEST_UCALL_FAILED,"Guest failed to allocate ucall struct");- memcpy(uc, addr, sizeof(*uc)); vcpu_run_complete_io(vcpu); } else {
base-commit: dc2efbe4813e0dc4368779bc36c5f0e636cb8eb2