On Wed, Aug 04, 2021, Maxim Levitsky wrote:
> Hi!
>
> I recently triaged a series of failures that I am seeing on both of my AMD machines in the kvm selftests.
>
> One test failed due to a trivial typo, to which I had sent a fix, but most of the other tests failed
> due to what I now suspect to be a very minor but still a CPU bug.
>
> All of the failing tests except two tests that timeout (and I haven't yet triaged them),
> use the perf_test_util.c library.
> All of these fail with SHUTDOWN exit reason.
>
> After a relatively recent commit ef4c9f4f6546 ("KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()"),
> vm_get_max_gfn() was fixed to return the maximum GFN that the guest can use.
> For default VM type this value is obtained from 'vm->pa_bit's which is in turn obtained
> from guest's cpuid in kvm_get_cpu_address_width function.
>
> It is 48 on both my AMD machines (3970X and 4650U) and also on remote EPYC 7302P machine.
> (all of them are Zen2 machines)
>
> My 3970X has SME enabled by BIOS, while my 4650U doesn't have it enabled.
> The 7302P also has SME enabled.
> SEV was obviously not enabled for the test.
> NPT was enabled.
>
> It appears that if the guest uses any GPA above 0xFFFCFFFFF000 in its guest paging tables,
> then it gets #PF with reserved bits error code.
LOL, I encountered this joy a few weeks back. There's a magic Hyper-Transport
region at the top of memory that is reserved, even for GPAs. You and I say
"CPU BUG!!!", AMD says "working as intended" ;-)
https://lkml.kernel.org/r/20210625020354.431829-2-seanjc@xxxxxxxxxx
