Re: [PATCH 2/3] selftests: kvm: s390: Add uc_skey VM test case

[Christoph Schlameuss <schlameuss@linux.ibm.com>]

On Fri Aug 16, 2024 at 4:36 PM CEST, Janosch Frank wrote:
> On 8/15/24 5:45 PM, Christoph Schlameuss wrote:
> > Add a test case manipulating s390 storage keys from within the ucontrol
> > VM.
> > 
> > Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
> > ---
> >   .../selftests/kvm/s390x/ucontrol_test.c       | 76 +++++++++++++++++++
> >   1 file changed, 76 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/kvm/s390x/ucontrol_test.c b/tools/testing/selftests/kvm/s390x/ucontrol_test.c
> > index 41306bb52f29..5f8815a80544 100644
> > --- a/tools/testing/selftests/kvm/s390x/ucontrol_test.c
> > +++ b/tools/testing/selftests/kvm/s390x/ucontrol_test.c
> > @@ -79,6 +79,32 @@ asm("test_mem_asm:\n"
> >   	"	j	0b\n"
> >   );
> >   
> > +/* Test program manipulating storage keys */
> > +extern char test_skey_asm[];
> > +asm("test_skey_asm:\n"
> > +	"xgr	%r0, %r0\n"
> > +
> > +	"0:\n"
> > +	"	ahi	%r0,1\n"
> > +	"	st	%r1,0(%r5,%r6)\n"
> > +
> > +	"	iske	%r1,%r6\n"
> > +	"	ahi	%r0,1\n"
> > +	"	diag	0,0,0x44\n"
> > +
> > +	"	sske	%r1,%r6\n"
>
> Might want to add a xgr here so you're sure that you're not reading your 
> own values if iske fails.
>

Good point. Will change the r1 value here.

> > +	"	iske	%r1,%r6\n"
> > +	"	ahi	%r0,1\n"
> > +	"	diag	0,0,0x44\n"
> > +
> > +	"	rrbe	%r1,%r6\n"
> > +	"	iske	%r1,%r6\n"
> > +	"	ahi	%r0,1\n"
> > +	"	diag	0,0,0x44\n"
> > +
> > +	"	j	0b\n"
> > +);
> > +
> >   FIXTURE(uc_kvm)
> >   {
> >   	struct kvm_s390_sie_block *sie_block;
> > @@ -345,6 +371,56 @@ static void uc_assert_diag44(FIXTURE_DATA(uc_kvm) * self)
> >   	TEST_ASSERT_EQ(0x440000, sie_block->ipb);
> >   }
> >   
> > +TEST_F(uc_kvm, uc_skey)
> > +{
> > +	u64 test_vaddr = self->base_gpa + VM_MEM_SIZE - (SZ_1M / 2);
> > +	struct kvm_sync_regs *sync_regs = &self->run->s.regs;
> > +	struct kvm_run *run = self->run;
> > +	u8 skeyvalue = 0x34;
> > +
> > +	/* copy test_skey_asm to code_hva / code_gpa */
> > +	TH_LOG("copy code %p to vm mapped memory %p / %p",
> > +	       &test_skey_asm, (void *)self->code_hva, (void *)self->code_gpa);
> > +	memcpy((void *)self->code_hva, &test_skey_asm, PAGE_SIZE);
> > +
> > +	/* set register content for test_skey_asm to access not mapped memory */
> > +	sync_regs->gprs[1] = skeyvalue;
> > +	sync_regs->gprs[5] = self->base_gpa;
> > +	sync_regs->gprs[6] = test_vaddr;
> > +	run->kvm_dirty_regs |= KVM_SYNC_GPRS;
> > +
> > +	self->sie_block->ictl |= ICTL_OPEREXC | ICTL_PINT;
> > +	self->sie_block->cpuflags &= ~CPUSTAT_KSS;
>
> So you don't want KVM to initialize skeys?
> Or am I missing a ucontrol skey interaction?
>
> What about the ICTLs if KSS is not available on the machine?

This is explicitly disabling KSS, not enabling it.
Doing that explicitly might not strictly be necessary but I thought this does
provide some clarity about the state.