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

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.