From: Marc Zyngier maz@kernel.org
mainline inclusion from mainline-v6.8-rc1 commit 103423ad7e56d6c756738823c332c414b07899e6 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9GCZS CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Back in 2016, it was argued that implementations lacking a HW prefetcher could be helped by sprinkling a number of PRFM instructions in strategic locations.
In 2023, the one platform that presumably needed this hack is no longer in active use (let alone maintained), and an quick experiment shows dropping this hack only leads to a 0.4% drop on a full kernel compilation (tested on a MT30-GS0 48 CPU system).
Given that this is pretty much in the noise department and that it may give odd ideas to other implementers, drop the hack for good.
Suggested-by: Will Deacon will@kernel.org Suggested-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Marc Zyngier maz@kernel.org Acked-by: Catalin Marinas catalin.marinas@arm.com Link: https://lore.kernel.org/r/20231122133754.1240687-1-maz@kernel.org Signed-off-by: Will Deacon will@kernel.org
conflicts: arch/arm64/kernel/cpufeature.c arch/arm64/tools/cpucaps
Signed-off-by: Tong Tiangen tongtiangen@huawei.com --- arch/arm64/kernel/cpufeature.c | 16 ---------------- arch/arm64/lib/copy_page.S | 11 ----------- arch/arm64/tools/cpucaps | 1 - 3 files changed, 28 deletions(-)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 316c57b19c93..c0d5985012d7 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1582,16 +1582,6 @@ static bool has_useable_gicv3_cpuif(const struct arm64_cpu_capabilities *entry, return has_sre; }
-static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry, int __unused) -{ - u32 midr = read_cpuid_id(); - - /* Cavium ThunderX pass 1.x and 2.x */ - return midr_is_cpu_model_range(midr, MIDR_THUNDERX, - MIDR_CPU_VAR_REV(0, 0), - MIDR_CPU_VAR_REV(1, MIDR_REVISION_MASK)); -} - static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unused) { u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1); @@ -2401,12 +2391,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { ARM64_CPUID_FIELDS(ID_AA64ISAR0_EL1, ATOMIC, IMP) }, #endif /* CONFIG_ARM64_LSE_ATOMICS */ - { - .desc = "Software prefetching using PRFM", - .capability = ARM64_HAS_NO_HW_PREFETCH, - .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, - .matches = has_no_hw_prefetch, - }, { .desc = "Virtualization Host Extensions", .capability = ARM64_HAS_VIRT_HOST_EXTN, diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S index c336d2ffdec5..6a56d7cf309d 100644 --- a/arch/arm64/lib/copy_page.S +++ b/arch/arm64/lib/copy_page.S @@ -18,13 +18,6 @@ * x1 - src */ SYM_FUNC_START(__pi_copy_page) -alternative_if ARM64_HAS_NO_HW_PREFETCH - // Prefetch three cache lines ahead. - prfm pldl1strm, [x1, #128] - prfm pldl1strm, [x1, #256] - prfm pldl1strm, [x1, #384] -alternative_else_nop_endif - ldp x2, x3, [x1] ldp x4, x5, [x1, #16] ldp x6, x7, [x1, #32] @@ -39,10 +32,6 @@ alternative_else_nop_endif 1: tst x0, #(PAGE_SIZE - 1)
-alternative_if ARM64_HAS_NO_HW_PREFETCH - prfm pldl1strm, [x1, #384] -alternative_else_nop_endif - stnp x2, x3, [x0, #-256] ldp x2, x3, [x1] stnp x4, x5, [x0, #16 - 256] diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps index f5e1e494ba84..2d3df8c73158 100644 --- a/arch/arm64/tools/cpucaps +++ b/arch/arm64/tools/cpucaps @@ -41,7 +41,6 @@ HAS_MOPS HAS_NESTED_VIRT HAS_NMI HAS_NO_FPSIMD -HAS_NO_HW_PREFETCH HAS_PAN HAS_S1PIE HAS_RAS_EXTN