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Diffstat (limited to 'arch/x86/include/asm/sync_core.h')
-rw-r--r-- | arch/x86/include/asm/sync_core.h | 111 |
1 files changed, 111 insertions, 0 deletions
diff --git a/arch/x86/include/asm/sync_core.h b/arch/x86/include/asm/sync_core.h new file mode 100644 index 0000000000..ab7382f92a --- /dev/null +++ b/arch/x86/include/asm/sync_core.h @@ -0,0 +1,111 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_X86_SYNC_CORE_H +#define _ASM_X86_SYNC_CORE_H + +#include <linux/preempt.h> +#include <asm/processor.h> +#include <asm/cpufeature.h> +#include <asm/special_insns.h> + +#ifdef CONFIG_X86_32 +static inline void iret_to_self(void) +{ + asm volatile ( + "pushfl\n\t" + "pushl %%cs\n\t" + "pushl $1f\n\t" + "iret\n\t" + "1:" + : ASM_CALL_CONSTRAINT : : "memory"); +} +#else +static inline void iret_to_self(void) +{ + unsigned int tmp; + + asm volatile ( + "mov %%ss, %0\n\t" + "pushq %q0\n\t" + "pushq %%rsp\n\t" + "addq $8, (%%rsp)\n\t" + "pushfq\n\t" + "mov %%cs, %0\n\t" + "pushq %q0\n\t" + "pushq $1f\n\t" + "iretq\n\t" + "1:" + : "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory"); +} +#endif /* CONFIG_X86_32 */ + +/* + * This function forces the icache and prefetched instruction stream to + * catch up with reality in two very specific cases: + * + * a) Text was modified using one virtual address and is about to be executed + * from the same physical page at a different virtual address. + * + * b) Text was modified on a different CPU, may subsequently be + * executed on this CPU, and you want to make sure the new version + * gets executed. This generally means you're calling this in an IPI. + * + * If you're calling this for a different reason, you're probably doing + * it wrong. + * + * Like all of Linux's memory ordering operations, this is a + * compiler barrier as well. + */ +static inline void sync_core(void) +{ + /* + * The SERIALIZE instruction is the most straightforward way to + * do this, but it is not universally available. + */ + if (static_cpu_has(X86_FEATURE_SERIALIZE)) { + serialize(); + return; + } + + /* + * For all other processors, there are quite a few ways to do this. + * IRET-to-self is nice because it works on every CPU, at any CPL + * (so it's compatible with paravirtualization), and it never exits + * to a hypervisor. The only downsides are that it's a bit slow + * (it seems to be a bit more than 2x slower than the fastest + * options) and that it unmasks NMIs. The "push %cs" is needed, + * because in paravirtual environments __KERNEL_CS may not be a + * valid CS value when we do IRET directly. + * + * In case NMI unmasking or performance ever becomes a problem, + * the next best option appears to be MOV-to-CR2 and an + * unconditional jump. That sequence also works on all CPUs, + * but it will fault at CPL3 (i.e. Xen PV). + * + * CPUID is the conventional way, but it's nasty: it doesn't + * exist on some 486-like CPUs, and it usually exits to a + * hypervisor. + */ + iret_to_self(); +} + +/* + * Ensure that a core serializing instruction is issued before returning + * to user-mode. x86 implements return to user-space through sysexit, + * sysrel, and sysretq, which are not core serializing. + */ +static inline void sync_core_before_usermode(void) +{ + /* With PTI, we unconditionally serialize before running user code. */ + if (static_cpu_has(X86_FEATURE_PTI)) + return; + + /* + * Even if we're in an interrupt, we might reschedule before returning, + * in which case we could switch to a different thread in the same mm + * and return using SYSRET or SYSEXIT. Instead of trying to keep + * track of our need to sync the core, just sync right away. + */ + sync_core(); +} + +#endif /* _ASM_X86_SYNC_CORE_H */ |