Re: [RFC PATCH v1 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access

[Christian Borntraeger]

Am 19.01.22 um 12:52 schrieb Thomas Huth:
> On 18/01/2022 10.52, Janis Schoetterl-Glausch wrote:
> > Channel I/O honors storage keys and is performed on absolute memory.
> > For I/O emulation user space therefore needs to be able to do key
> > checked accesses.
>
> Can't we do the checking in userspace? We already have functions for handling the storage keys there (see hw/s390x/s390-skeys-kvm.c), so why can't we do the checking in QEMU?

That would separate the key check from the memory operation. Potentially for a long time.
Wenn we piggy back on access_guest_abs_with_key we use mvcos in the host and thus do the key check in lockstep with the keycheck which is the preferrable solution.

I would also like to avoid reading guest storage keys via the ioctl that was done for migration in the I/O path just to do a single key check. This has peformance concerns.