[PATCH v3 06/18] KVM: arm64: nv: Enforce S2 alignment when contiguous bit is set

Marc Zyngier
2024-08-13T10:06:22Z

Despite KVM not using the contiguous bit for anything related to
TLBs, the spec does require that the alignment defined by the
contiguous bit for a the page size and the level is enforced.

Add the required checks to offset the point where PA and VA merge.

Fixes: 61e30b9eef7f ("KVM: arm64: nv: Implement nested Stage-2 page table walk logic")
Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/kvm_nested.h | 22 ++++++++++++++++++++++
arch/arm64/kvm/nested.c | 7 ++-----
2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 5b06c31035a2..6e163501f13e 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -205,4 +205,26 @@ static inline u64 kvm_encode_nested_level(struct kvm_s2_trans *trans)
return FIELD_PREP(KVM_NV_GUEST_MAP_SZ, trans->level);
}

+/* Adjust alignment for the contiguous bit as per StageOA() */
+#define contiguous_bit_shift(d, wi, l) \
+ ({ \
+ u8 shift = 0; \
+ \
+ if ((d) & PTE_CONT) { \
+ switch (BIT((wi)->pgshift)) { \
+ case SZ_4K: \
+ shift = 4; \
+ break; \
+ case SZ_16K: \
+ shift = (l) == 2 ? 5 : 7; \
+ break; \
+ case SZ_64K: \
+ shift = 5; \
+ break; \
+ } \
+ } \
+ \
+ shift; \
+ })
+
#endif /* __ARM64_KVM_NESTED_H */
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index de789e0f1ae9..49a7832a3fb1 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -282,11 +282,6 @@ static int walk_nested_s2_pgd(phys_addr_t ipa,
return 1;
}

- /*
- * We don't use the contiguous bit in the stage-2 ptes, so skip check
- * for misprogramming of the contiguous bit.
- */
-
if (check_output_size(wi, desc)) {
out->esr = compute_fsc(level, ESR_ELx_FSC_ADDRSZ);
out->upper_attr = desc;
@@ -299,6 +294,8 @@ static int walk_nested_s2_pgd(phys_addr_t ipa,
return 1;
}

+ addr_bottom += contiguous_bit_shift(desc, wi, level);
+
/* Calculate and return the result */
paddr = (desc & GENMASK_ULL(47, addr_bottom)) |
(ipa & GENMASK_ULL(addr_bottom - 1, 0));
--
2.39.2