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 ARM ARM DDI0487L.a B2.2.6 (Possible implementation restrictions on using atomic instructions), atomic instructions are architecturally guaranteed for Inner Shareable and Outer Shareable attributes. For Non-Shareable attribute, the atomic instructions are not atomic and issuing such an instruction can lead to the FSC mentioned in this case (among other things). Moreover, 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 Neoverse-N3 chose to implement these two and why we see an FSC of 0x35 in EL1 upon executing atomic instructions. ARM64 KVM selftests sets no shareable attributes, which makes them Non-Shareable by default. Hence, explicitly set them as Inner-Shareable to fix this issue. Suggested-by: Oliver Upton <oupton@xxxxxxxxxx> Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx> --- 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 7d88ff22013a..b0fc0f945766 100644 --- 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 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
