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| author | Catalin Marinas <catalin.marinas@arm.com> | 2024-12-03 15:19:41 +0000 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2024-12-05 11:24:38 +0000 |
| commit | c0900d15d31c2597dd9f634c8be2b71762199890 (patch) | |
| tree | ae29c93dc839074a70b5214fa6d95c9b9fd83b6c /arch/arm64 | |
| parent | c2b46ae022704a2d845e59461fa24431ad627022 (diff) | |
| download | lwn-c0900d15d31c2597dd9f634c8be2b71762199890.tar.gz lwn-c0900d15d31c2597dd9f634c8be2b71762199890.zip | |
arm64: Ensure bits ASID[15:8] are masked out when the kernel uses 8-bit ASIDs
Linux currently sets the TCR_EL1.AS bit unconditionally during CPU
bring-up. On an 8-bit ASID CPU, this is RES0 and ignored, otherwise
16-bit ASIDs are enabled. However, if running in a VM and the hypervisor
reports 8-bit ASIDs (ID_AA64MMFR0_EL1.ASIDBits == 0) on a 16-bit ASIDs
CPU, Linux uses bits 8 to 63 as a generation number for tracking old
process ASIDs. The bottom 8 bits of this generation end up being written
to TTBR1_EL1 and also used for the ASID-based TLBI operations as the
upper 8 bits of the ASID. Following an ASID roll-over event we can have
threads of the same application with the same 8-bit ASID but different
generation numbers running on separate CPUs. Both TLB caching and the
TLBI operations will end up using different actual 16-bit ASIDs for the
same process.
A similar scenario can happen in a big.LITTLE configuration if the boot
CPU only uses 8-bit ASIDs while secondary CPUs have 16-bit ASIDs.
Ensure that the ASID generation is only tracked by bits 16 and up,
leaving bits 15:8 as 0 if the kernel uses 8-bit ASIDs. Note that
clearing TCR_EL1.AS is not sufficient since the architecture requires
that the top 8 bits of the ASID passed to TLBI instructions are 0 rather
than ignored in such configuration.
Cc: stable@vger.kernel.org
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241203151941.353796-1-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64')
| -rw-r--r-- | arch/arm64/mm/context.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index 188197590fc9..b2ac06246327 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -32,9 +32,9 @@ static unsigned long nr_pinned_asids; static unsigned long *pinned_asid_map; #define ASID_MASK (~GENMASK(asid_bits - 1, 0)) -#define ASID_FIRST_VERSION (1UL << asid_bits) +#define ASID_FIRST_VERSION (1UL << 16) -#define NUM_USER_ASIDS ASID_FIRST_VERSION +#define NUM_USER_ASIDS (1UL << asid_bits) #define ctxid2asid(asid) ((asid) & ~ASID_MASK) #define asid2ctxid(asid, genid) ((asid) | (genid)) |