Re: [PATCH 1/5] KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest

On 20/08/21 20:51, Mathieu Desnoyers wrote:

quoted

Ah, or is it the case that rseq_cs is non-NULL if and only if userspace is in an
rseq critical section, and because syscalls in critical sections are illegal, by
definition clearing rseq_cs is a nop unless userspace is misbehaving.

Not quite, as I described above. But we want it to stay set so the CONFIG_DEBUG_RSEQ
code executed when returning from ioctl to userspace will be able to validate that
it is not nested within a rseq critical section.

quoted

If that's true, what about explicitly checking that at NOTIFY_RESUME?  Or is it
not worth the extra code to detect an error that will likely be caught anyways?

The error will indeed already be caught on return from ioctl to userspace, so I
don't see any added value in duplicating this check.

Sean, can you send a v2 (even for this patch only would be okay)?

Thanks,

Paolo