[PATCH 2/2] KVM: selftests: arm64: Explicitly set the page attrs to Inner-Shareable

[Raghavendra Rao Ananta]

Atomic instructions such as 'ldset' over (global) variables in the guest
is observed to cause an EL1 data abort with FSC 0x35 (IMPLEMENTATION
DEFINED fault (Unsupported Exclusive or Atomic access)). The observation
was particularly apparent on Neoverse-N3.

According to DDI0487L.a C3.2.6 (Single-copy atomic 64-byte load/store),
it is implementation defined that a data abort with the mentioned FSC
is reported for the first stage of translation that provides an
inappropriate memory type. It's likely that the same rule also applies
to memory attribute mismatch. When the guest loads the memory location of
the variable that was already cached during the host userspace's copying
of the ELF into the memory, the core is likely running into a mismatch
of memory attrs that's checked in stage-1 itself, and thus causing the
abort in EL1.

Fix this by explicitly setting the memory attribute to Inner-Shareable
to avoid the mismatch, and by extension, the data abort.

Suggested-by: Oliver Upton <oupton at google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta at google.com>
---
 tools/testing/selftests/kvm/include/arm64/processor.h | 1 +
 tools/testing/selftests/kvm/lib/arm64/processor.c     | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/arm64/processor.h b/tools/testing/selftests/kvm/include/arm64/processor.h
index 691670bbe226..b337a606aac4 100644
--- a/tools/testing/selftests/kvm/include/arm64/processor.h
+++ b/tools/testing/selftests/kvm/include/arm64/processor.h
@@ -75,6 +75,7 @@
 #define PMD_TYPE_TABLE		BIT(1)
 #define PTE_TYPE_PAGE		BIT(1)
 
+#define PTE_SHARED		(UL(3) << 8) /* SH[1:0], inner shareable */
 #define PTE_AF			BIT(10)
 
 #define PTE_ADDR_MASK(page_shift)	GENMASK(47, (page_shift))
diff --git a/tools/testing/selftests/kvm/lib/arm64/processor.c b/tools/testing/selftests/kvm/lib/arm64/processor.c
index da5802c8a59c..9d69904cb608 100644
--- a/tools/testing/selftests/kvm/lib/arm64/processor.c
+++ b/tools/testing/selftests/kvm/lib/arm64/processor.c
@@ -172,6 +172,9 @@ static void _virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr,
 	}
 
 	pg_attr = PTE_AF | PTE_ATTRINDX(attr_idx) | PTE_TYPE_PAGE | PTE_VALID;
+	if (!use_lpa2_pte_format(vm))
+		pg_attr |= PTE_SHARED;
+
 	*ptep = addr_pte(vm, paddr, pg_attr);
 }
 
-- 
2.49.0.504.g3bcea36a83-goog