From a11dd731f5ead63ab3d757bbb1ab631063f6c034 Mon Sep 17 00:00:00 2001 From: Russell King Date: Fri, 4 Jul 2014 14:44:36 +0100 Subject: ARM: SWP emulation: always enable when SMP is enabled SWP is deprecated in ARMv6 and ARMv7 CPUs, but more importantly, when running on a SMP system, SWP doesn't guarantee atomicity. This means it can't really be used (by userspace) for locking purposes in a SMP environment. Currently, many configurations leave the SWP emulation disabled, which means we never know if userspace executes this instruction on ARMv7 hardware. Rectify this by enabling SWP emulation for ARMv7 with SMP (where we can trap the instruction.) Tested-by: Tony Lindgren Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/mm/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/arm') diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index c348eaee7ee2..c78c7db6aa83 100644 --- a/arch/arm/mm/Kconfig +++ b/arch/arm/mm/Kconfig @@ -669,7 +669,7 @@ config ARM_VIRT_EXT details. config SWP_EMULATE - bool "Emulate SWP/SWPB instructions" + bool "Emulate SWP/SWPB instructions" if !SMP depends on CPU_V7 default y if SMP select HAVE_PROC_CPU if PROC_FS -- cgit From 7397aa48fff47c2386867a3fbfce8f3e664843a9 Mon Sep 17 00:00:00 2001 From: Russell King Date: Fri, 4 Jul 2014 14:49:05 +0100 Subject: ARM: SWP emulation: only initialise on ARMv7 CPUs Previous CPUs do not have the ability to trap SWP instructions, so it's pointless initialising this code there. Tested-by: Tony Lindgren Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/kernel/swp_emulate.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/arm') diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c index b1b89882b113..67ca8578c6d8 100644 --- a/arch/arm/kernel/swp_emulate.c +++ b/arch/arm/kernel/swp_emulate.c @@ -27,6 +27,7 @@ #include #include +#include #include #include @@ -266,6 +267,9 @@ static struct undef_hook swp_hook = { */ static int __init swp_emulation_init(void) { + if (cpu_architecture() < CPU_ARCH_ARMv7) + return 0; + #ifdef CONFIG_PROC_FS if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops)) return -ENOMEM; -- cgit From 58171bf2af6b547a560b304f6ab2b9edf1c31d5a Mon Sep 17 00:00:00 2001 From: Russell King Date: Fri, 4 Jul 2014 16:41:21 +0100 Subject: ARM: hwcap: disable HWCAP_SWP if the CPU advertises it has exclusives When the CPU has support for the byte and word exclusive operations, userspace should use them in preference to the SWP instructions. Detect the presence of these instructions by reading the ISAR CPU ID registers and adjust the ELF HWCAP mask appropriately. Note that ARM1136 < r1p0 has no ISAR4, so this is explicitly detected and the test disabled, leaving the current situation where HWCAP_SWP is set. Tested-by: Tony Lindgren Acked-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/kernel/setup.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) (limited to 'arch/arm') diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index 8a16ee5d8a95..84db893dedc2 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -393,19 +393,34 @@ static void __init cpuid_init_hwcaps(void) elf_hwcap |= HWCAP_LPAE; } -static void __init feat_v6_fixup(void) +static void __init elf_hwcap_fixup(void) { - int id = read_cpuid_id(); - - if ((id & 0xff0f0000) != 0x41070000) - return; + unsigned id = read_cpuid_id(); + unsigned sync_prim; /* * HWCAP_TLS is available only on 1136 r1p0 and later, * see also kuser_get_tls_init. */ - if ((((id >> 4) & 0xfff) == 0xb36) && (((id >> 20) & 3) == 0)) + if (read_cpuid_part() == ARM_CPU_PART_ARM1136 && + ((id >> 20) & 3) == 0) { elf_hwcap &= ~HWCAP_TLS; + return; + } + + /* Verify if CPUID scheme is implemented */ + if ((id & 0x000f0000) != 0x000f0000) + return; + + /* + * If the CPU supports LDREX/STREX and LDREXB/STREXB, + * avoid advertising SWP; it may not be atomic with + * multiprocessing cores. + */ + sync_prim = ((read_cpuid_ext(CPUID_EXT_ISAR3) >> 8) & 0xf0) | + ((read_cpuid_ext(CPUID_EXT_ISAR4) >> 20) & 0x0f); + if (sync_prim >= 0x13) + elf_hwcap &= ~HWCAP_SWP; } /* @@ -609,7 +624,7 @@ static void __init setup_processor(void) #endif erratum_a15_798181_init(); - feat_v6_fixup(); + elf_hwcap_fixup(); cacheid_init(); cpu_init(); -- cgit