On Tue, Aug 04, 2020 at 07:10:59PM -0700, Ricardo Neri wrote:
> The SERIALIZE instruction gives software a way to force the processor to
> complete all modifications to flags, registers and memory from previous
> instructions and drain all buffered writes to memory before the next
> instruction is fetched and executed. Thus, it serves the purpose of
> sync_core(). Use it when available.
>
> Commit 7117f16bf460 ("objtool: Fix ORC vs alternatives") enforced stack
> invariance in alternatives. The iret-to-self does not comply with such
> invariance. Thus, it cannot be used inside alternative code. Instead, use
> an alternative that jumps to SERIALIZE when available.
>
> Cc: Andy Lutomirski <l...@kernel.org>
> Cc: Cathy Zhang <cathy.zh...@intel.com>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: Fenghua Yu <fenghua...@intel.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Kyung Min Park <kyung.min.p...@intel.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: "Ravi V. Shankar" <ravi.v.shan...@intel.com>
> Cc: Sean Christopherson <sean.j.christopher...@intel.com>
> Cc: linux-e...@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Suggested-by: Andy Lutomirski <l...@kernel.org>
> Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com>
> ---
> This is a v2 from my initial submission [1]. The first three patches of
> the series have been merged in Linus' tree. Hence, I am submitting only
> this patch for review.
>
> [1]. https://lkml.org/lkml/2020/7/27/8
>
> Changes since v1:
> * Support SERIALIZE using alternative runtime patching.
> (Peter Zijlstra, H. Peter Anvin)
> * Added a note to specify which version of binutils supports SERIALIZE.
> (Peter Zijlstra)
> * Verified that (::: "memory") is used. (H. Peter Anvin)
> ---
> arch/x86/include/asm/special_insns.h | 2 ++
> arch/x86/include/asm/sync_core.h | 10 +++++++++-
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/special_insns.h
> b/arch/x86/include/asm/special_insns.h
> index 59a3e13204c3..25cd67801dda 100644
> --- a/arch/x86/include/asm/special_insns.h
> +++ b/arch/x86/include/asm/special_insns.h
> @@ -10,6 +10,8 @@
> #include <linux/irqflags.h>
> #include <linux/jump_label.h>
>
> +/* Instruction opcode for SERIALIZE; supported in binutils >= 2.35. */
> +#define __ASM_SERIALIZE ".byte 0xf, 0x1, 0xe8"
> /*
> * Volatile isn't enough to prevent the compiler from reordering the
> * read/write functions for the control registers and messing everything up.
> diff --git a/arch/x86/include/asm/sync_core.h
> b/arch/x86/include/asm/sync_core.h
> index fdb5b356e59b..201ea3d9a6bd 100644
> --- a/arch/x86/include/asm/sync_core.h
> +++ b/arch/x86/include/asm/sync_core.h
> @@ -5,15 +5,19 @@
> #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 (
> + ALTERNATIVE("", "jmp 2f", X86_FEATURE_SERIALIZE)
> "pushfl\n\t"
> "pushl %%cs\n\t"
> "pushl $1f\n\t"
> "iret\n\t"
> + "2:\n\t"
> + __ASM_SERIALIZE "\n"
> "1:"
> : ASM_CALL_CONSTRAINT : : "memory");
> }
> @@ -23,6 +27,7 @@ static inline void iret_to_self(void)
> unsigned int tmp;
>
> asm volatile (
> + ALTERNATIVE("", "jmp 2f", X86_FEATURE_SERIALIZE)
Why is this and above stuck inside the asm statement?
Why can't you simply do:
if (static_cpu_has(X86_FEATURE_SERIALIZE)) {
asm volatile(__ASM_SERIALIZE ::: "memory");
return;
}
on function entry instead of making it more unreadable for no particular
reason?
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Mary Higgins, Sri Rasiah, HRB 21284 (AG
Nürnberg)
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