From: Jason Gunthorpe Date: Thu, 15 Jan 2026 18:23:30 +0000 (-0800) Subject: iommu/arm-smmu-v3: Mark EATS_TRANS safe when computing the update sequence X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7cad800485956a263318930613f8f4a084af8c70;p=thirdparty%2Fkernel%2Flinux.git iommu/arm-smmu-v3: Mark EATS_TRANS safe when computing the update sequence If VM wants to toggle EATS_TRANS off at the same time as changing the CFG, hypervisor will see EATS change to 0 and insert a V=0 breaking update into the STE even though the VM did not ask for that. In bare metal, EATS_TRANS is ignored by CFG=ABORT/BYPASS, which is why this does not cause a problem until we have the nested case where CFG is always a variation of S2 trans that does use EATS_TRANS. Relax the rules for EATS_TRANS sequencing, we don't need it to be exact as the enclosing code will always disable ATS at the PCI device when changing EATS_TRANS. This ensures there are no ATS transactions that can race with an EATS_TRANS change so we don't need to carefully sequence these bits. Fixes: 1e8be08d1c91 ("iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED") Cc: stable@vger.kernel.org Signed-off-by: Jason Gunthorpe Reviewed-by: Shuai Xue Signed-off-by: Nicolin Chen Signed-off-by: Will Deacon --- diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c index 3ab0f047c8927..8523798453598 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -1097,6 +1097,32 @@ VISIBLE_IF_KUNIT void arm_smmu_get_ste_update_safe(const __le64 *cur, const __le64 *target, __le64 *safe_bits) { + const __le64 eats_s1chk = + FIELD_PREP(STRTAB_STE_1_EATS, STRTAB_STE_1_EATS_S1CHK); + const __le64 eats_trans = + FIELD_PREP(STRTAB_STE_1_EATS, STRTAB_STE_1_EATS_TRANS); + + /* + * When an STE changes EATS_TRANS, the sequencing code in the attach + * logic already will have the PCI cap for ATS disabled. Thus at this + * moment we can expect that the device will not generate ATS queries + * and so we don't care about the sequencing of EATS. The purpose of + * EATS_TRANS is to protect the system from hostile untrusted devices + * that issue ATS when the PCI config space is disabled. However, if + * EATS_TRANS is being changed, then we must have already trusted the + * device as the EATS_TRANS security block is being disabled. + * + * Note: now the EATS_TRANS update is moved to the first entry_set(). + * Changing S2S and EATS might transiently result in S2S=1 and EATS=1 + * which is a bad STE (see "5.2 Stream Table Entry"). In such a case, + * we can't do a hitless update. Also, it should not be added to the + * safe bits with STRTAB_STE_1_EATS_S1CHK, because EATS=0b11 would be + * effectively an errant 0b00 configuration. + */ + if (!((cur[1] | target[1]) & cpu_to_le64(eats_s1chk)) && + !((cur[2] | target[2]) & cpu_to_le64(STRTAB_STE_2_S2S))) + safe_bits[1] |= cpu_to_le64(eats_trans); + /* * MEV does not meaningfully impact the operation of the HW, it only * changes how many fault events are generated, thus we can relax it