Re: [PATCH v5 07/10] selftests: kvm: s390: Add uc_map_unmap VM test case

Christoph Schlameuss
2024-08-13T10:59:07Z

On Tue, Aug 13, 2024 at 09:21:12AM +0200, Janosch Frank wrote:
> On 8/7/24 5:45 PM, Christoph Schlameuss wrote:
> > Add a test case verifying basic running and interaction of ucontrol VMs.
> > Fill the segment and page tables for allocated memory and map memory on
> > first access.
> >
> > * uc_map_unmap
> > Store and load data to mapped and unmapped memory and use pic segment
> > translation handling to map memory on access.
> >
> > Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
> > ---
> > .../selftests/kvm/s390x/ucontrol_test.c | 167 +++++++++++++++++-
> > 1 file changed, 166 insertions(+), 1 deletion(-)
> >
>
> [...]
>
> > +static void init_st_pt(FIXTURE_DATA(uc_kvm) * self)
> > +{
> > + struct kvm_sync_regs *sync_regs = &self->run->s.regs;
> > + u64 first_pt_addr, ste, s_addr, pte;
> > + struct kvm_run *run = self->run;
> > + void *se_addr;
> > + int si, pi;
> > + u64 *phd;
> > +
> > + /* set PASCE addr */
> > + self->pgd = self->base_gpa + SZ_1M;
> > + phd = gpa2hva(self, self->pgd);
> > + memset(phd, 0xff, VM_MEM_TABLE_SIZE);
> > +
> > + first_pt_addr = self->pgd + (VM_MEM_TABLE_SIZE * VM_MEM_MAX_M);
> > + /* for each segment in the VM */
> > + for (si = 0; si < VM_MEM_MAX_M; si++) {
> > + /* build segment table entry (ste) */
> > + ste = (first_pt_addr + (VM_MEM_TABLE_SIZE * si)) & ~0x7fful;
> > + /* store ste in st */
> > + phd[si] = ste;
> > +
> > + se_addr = gpa2hva(self, phd[si]);
> > + s_addr = self->base_gpa + (si * SZ_1M);
> > + memset(se_addr, 0xff, VM_MEM_TABLE_SIZE);
> > + /* for each page in the segment (VM) */
> > + for (pi = 0; pi < (SZ_1M / PAGE_SIZE); pi++) {
> > + /* build page table entry (pte) */
> > + pte = (s_addr + (pi * PAGE_SIZE)) & ~0xffful;
> > + /* store pte in pt */
> > + ((u64 *)se_addr)[pi] = pte;
> > + }
> > + }
> > + pr_debug("segment table entry %p (0x%lx) --> %p\n",
> > + phd, phd[0], gpa2hva(self, (phd[0] & ~0x7fful)));
> > + print_hex_bytes("st", (u64)phd, 64);
> > + print_hex_bytes("pt", (u64)gpa2hva(self, phd[0]), 128);
> > +
> > + /* PASCE TT=00 for segment table */
> > + sync_regs->crs[1] = self->pgd | 0x3;
> > + run->kvm_dirty_regs |= KVM_SYNC_CRS;
> > +}
>
> Having a closer look at this I don't understand why we need to setup DAT in
> the guest. Also, the guest's memory easily fits in a couple of segment
> entries so you could set the table length TL in the ASCE to one page instead
> of 4.
>

I did only create the tables to be able to switch the DAT on and with that use a
PSW that is a bit more normal.
Switching the DAT off will work fine for the tests here without loosing any
coverage in KVM. So I will remove it here and in the skey test.