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

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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@xxxxxxxxxxxxx>
---
  .../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.





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