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Re: [Qemu-devel] [PATCH v2 10/11] tcg/mips: Make direct jump patching th
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH v2 10/11] tcg/mips: Make direct jump patching thread-safe |
Date: |
Fri, 22 Apr 2016 20:27:38 +0200 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On 2016-04-22 20:00, Sergey Fedorov wrote:
> On 22/04/16 19:51, Aurelien Jarno wrote:
> > On 2016-04-22 18:47, Aurelien Jarno wrote:
> >> On 2016-04-22 19:08, Sergey Fedorov wrote:
> >>> From: Sergey Fedorov <address@hidden>
> >>>
> >>> Ensure direct jump patching in MIPS is atomic by using
> >>> atomic_read()/atomic_set() for code patching.
> >>>
> >>> Signed-off-by: Sergey Fedorov <address@hidden>
> >>> Signed-off-by: Sergey Fedorov <address@hidden>
> >>> ---
> >>>
> >>> Changes in v2:
> >>> * s/atomic_write/atomic_set/
> >>>
> >>> tcg/mips/tcg-target.inc.c | 3 ++-
> >>> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/tcg/mips/tcg-target.inc.c b/tcg/mips/tcg-target.inc.c
> >>> index 682e19897db0..cefc0398018a 100644
> >>> --- a/tcg/mips/tcg-target.inc.c
> >>> +++ b/tcg/mips/tcg-target.inc.c
> >>> @@ -1886,6 +1886,7 @@ static void tcg_target_init(TCGContext *s)
> >>> void tb_set_jmp_target1(uintptr_t jmp_addr, uintptr_t addr)
> >>> {
> >>> uint32_t *ptr = (uint32_t *)jmp_addr;
> >>> - *ptr = deposit32(*ptr, 0, 26, addr >> 2);
> >>> + uint32_t insn = atomic_read(ptr);
> >>> + atomic_set(ptr, deposit32(insn, 0, 26, addr >> 2));
> >>> flush_icache_range(jmp_addr, jmp_addr + 4);
> >> Does it really make sense to read and write the value atomically? The
> >> resulting operation is still not atomic, something can happen in
> >> between.
> > Hmm, thinking more about that, given the only instruction used is "J",
> > we don't have to read the value, patch it and write it. We can directly
> > use something like (untested):
> >
> > atomic_set(ptr, (0x02 << 26) | (addr >> 2));
>
> Hmm, looking at "case INDEX_op_goto_tb:" in tcg_out_op() again I'm
> thinking about:
>
> atomic_set(ptr, deposit32(OPC_J, 0, 26, addr >> 2));
Oh right, I forgot when reviewing the patch that this code is actually
in tcg-target.inc.c, and that the OPC_J constant is available.
Your version looks good to me.
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
address@hidden http://www.aurel32.net
- [Qemu-devel] [PATCH v2 03/11] tci: Make direct jump patching thread-safe, (continued)
- [Qemu-devel] [PATCH v2 03/11] tci: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 04/11] tcg/ppc: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 05/11] tcg/i386: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 08/11] tcg/aarch64: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 11/11] tcg: Note requirement on atomic direct jump patching, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 06/11] tcg/s390: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- [Qemu-devel] [PATCH v2 10/11] tcg/mips: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
- Re: [Qemu-devel] [PATCH v2 10/11] tcg/mips: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
[Qemu-devel] [PATCH v2 07/11] tcg/arm: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
[Qemu-devel] [PATCH v2 09/11] tcg/sparc: Make direct jump patching thread-safe, Sergey Fedorov, 2016/04/22
Re: [Qemu-devel] [PATCH v2 00/11] tcg: Make direct jump patching thread-safe, Richard Henderson, 2016/04/24