Re: [kvm-unit-tests PATCH v2 1/1] s390x: add migration test for storage keys

[Nico Boehr <nrb@linux.ibm.com>]

On Mon, 2022-05-16 at 18:47 +0200, Janis Schoetterl-Glausch wrote:
> On 5/16/22 11:07, Nico Boehr wrote:
> > Upon migration, we expect storage keys being set by the guest to be
> > preserved,
> > so add a test for it.
> 
> "being set" implies that keys are set while the migration is going
> on.
> That's not the case, is it?

Fixed.

> > We keep 128 pages and set predictable storage keys. Then, we
> > migrate and check
> > they can be read back and the respective access restrictions are in
> > place when
> 
> ... check that they ...

Added that.

> 
> > the access key in the PSW doesn't match.
> 
> The latter half of the sentence doesn't apply anymore, now that you
> simplified the test.
> So maybe something like: ... and check that they can be read back and
> match the value
> originally set.

Fixed.

> > diff --git a/s390x/migration-skey.c b/s390x/migration-skey.c
> > new file mode 100644
> > index 000000000000..ee4622eb94ba
> > --- /dev/null
> > +++ b/s390x/migration-skey.c
> > @@ -0,0 +1,78 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Storage Key migration tests
> > + *
> > + * Copyright IBM Corp. 2022
> > + *
> > + * Authors:
> > + *  Nico Boehr <nrb@linux.ibm.com>
> > + */
> > +
> > +#include <libcflat.h>
> > +#include <asm/facility.h>
> > +#include <asm/page.h>
> > +#include <asm/mem.h>
> > +#include <asm/interrupt.h>
> > +#include <hardware.h>
> > +
> > +#define NUM_PAGES 128
> > +static uint8_t pagebuf[NUM_PAGES][PAGE_SIZE]
> > __attribute__((aligned(PAGE_SIZE)));
> > +
> > +static void test_migration(void)
> > +{
> > +       int i, key_to_set;
> > +       uint8_t *page;
> > +       union skey expected_key, actual_key;
> > +
> > +       for (i = 0; i < NUM_PAGES; i++) {
> > +               /*
> > +                * Storage keys are 7 bit, lowest bit is always
> > returned as zero
> > +                * by iske
> > +                */
> > +               key_to_set = i * 2;
> > +               set_storage_key(pagebuf[i], key_to_set, 1);
> > +       }
> > +
> > +       puts("Please migrate me, then press return\n");
> > +       (void)getchar();
> > +
> > +       for (i = 0; i < NUM_PAGES; i++) {
> > +               report_prefix_pushf("page %d", i);
> > +
> > +               page = &pagebuf[i][0];
> > +               actual_key.val = get_storage_key(page);
> 
> The page variable is kinda useless now, I'd just do
> get_storage_key(pagebuf[0]).

Removed.

> > +               expected_key.val = i * 2;
> > +
> > +               /* ignore reference bit */
> 
> Why? Are there any implicit references I'm missing?

Since the PoP specifies (p. 5-122):

"The record of references provided by the reference
bit is not necessarily accurate. However, in the major-
ity of situations, reference recording approximately
coincides with the related storage reference."

I don't really see a way to test this properly.

Maybe I missed something?