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

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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>
This commit is contained in:
Raghavendra Rao Ananta
2025-04-05 00:10:42 +00:00
committed by Oliver Upton
parent d8d78398e5
commit c8631ea59b
2 changed files with 4 additions and 0 deletions
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1
tools/testing/selftests/kvm/include/arm64/processor.h
View File

@@ -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))

3
tools/testing/selftests/kvm/lib/arm64/processor.c
View File

@@ -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);
}