Messages in this thread | | | Date | Wed, 6 Jul 2011 12:39:56 +0300 | Subject | Re: [PATCH 1/3] x86: drop unnecessary kernel_eflags variable from 64 bit. | From | Pekka Enberg <> |
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On Tue, Jul 5, 2011 at 4:00 PM, Ian Campbell <ian.campbell@citrix.com> wrote: > For no reason that I can determine 64 bit x86 saves the current eflags > in cpu_init purely for use in ret_from_fork. The equivalent 32 bit > code simply hard codes 0x0202 as the new EFLAGS which seems safer than > relying on a potentially arbitrary EFLAGS saved during cpu_init. > > Original i386 changeset > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=47a5c6fa0e204a2b63309c648bb2fde36836c826 > Original x86_64 changset > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=658fdbef66e5e9be79b457edc2cbbb3add840aa9 > > The only comment in the later indicates that it is following the > former, but not why it differs in this way.
Well lets ask Linus and Andi?
> This change makes 64 bit use the same mechanism to setup the initial > EFLAGS on fork. Note that 64 bit resets EFLAGS before calling > schedule_tail() as opposed to 32 bit which calls schedule_tail() > first. Therefore the correct value for EFLAGS has opposite IF > bit. This will be fixed in a subsequent patch. > > Signed-off-by: Ian Campbell <ian.campbell@citrix.com> > Cc: x86@kernel.org > --- > arch/x86/kernel/cpu/common.c | 4 ---- > arch/x86/kernel/entry_64.S | 2 +- > 2 files changed, 1 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 22a073d..178c3b4 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -1077,8 +1077,6 @@ void syscall_init(void) > X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|X86_EFLAGS_IOPL); > } > > -unsigned long kernel_eflags; > - > /* > * Copies of the original ist values from the tss are only accessed during > * debugging, no special alignment required. > @@ -1231,8 +1229,6 @@ void __cpuinit cpu_init(void) > fpu_init(); > xsave_init(); > > - raw_local_save_flags(kernel_eflags); > - > if (is_uv_system()) > uv_cpu_init(); > } > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index e13329d..b50d142 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -396,7 +396,7 @@ ENTRY(ret_from_fork) > > LOCK ; btr $TIF_FORK,TI_flags(%r8) > > - pushq_cfi kernel_eflags(%rip) > + pushq_cfi $0x0002 > popfq_cfi # reset kernel eflags > > call schedule_tail # rdi: 'prev' task parameter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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