KVM: arm64: selftests: Explicitly set the page attrs to Inner-Shareable

Atomic instructions such as 'ldset' in the guest have been observed to
cause an EL1 data abort with FSC 0x35 (IMPLEMENTATION DEFINED fault
(Unsupported Exclusive or Atomic access)) on Neoverse-N3.

Per DDI0487L.a B2.2.6, atomic instructions are only architecturally
guaranteed for Inner/Outer Shareable Normal Write-Back memory. For
anything else the behavior is IMPLEMENTATION DEFINED and can lose
atomicity, or, in this case, generate an abort.

It would appear that selftests sets up the stage-1 mappings as Non
Shareable, leading to the observed abort. Explicitly set the
Shareability field to Inner Shareable for non-LPA2 page tables. Note
that for the LPA2 page table format, translations for cacheable memory
inherit the shareability attribute of the PTW, i.e. TCR_ELx.SH{0,1}.

Suggested-by: Oliver Upton <oupton@google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
Link: https://lore.kernel.org/r/20250405001042.1470552-3-rananta@google.com
[oliver: Rephrase changelog]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/tools/testing/selftests/kvm/include/arm64/processor.h b/tools/testing/selftests/kvm/include/arm64/processor.h
index 7d88ff22013ab437efc97700efab41c21ba6e7c3..b0fc0f945766fe82db70bbab693990c0609282f9 100644 (file)
--- a/tools/testing/selftests/kvm/include/arm64/processor.h
+++ b/tools/testing/selftests/kvm/include/arm64/processor.h
@@ -113,6 +113,7 @@
 #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 da5802c8a59c1f161e87a46a1e429167356c86a1..9d69904cb6084a8bbb2fa16546fad3846fd21f86 100644 (file)
--- 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);
 }