On Mon, 2014-10-06 at 23:27 +0200, Borislav Petkov wrote:
> On Thu, Oct 02, 2014 at 11:20:12PM +0800, Chen Yucong wrote:
> > From: Chen Yucong <sla...@gmail.com>
> > Subject: [PATCH] x86, MCE, AMD: move invariant code out from loop body
> >
> > "mce_threshold_vector = amd_threshold_interrupt;" is loop invariant code
> > in mce_amd_feature_init(). So it should be moved out from loop body.
> >
> > Signed-off-by: Chen Yucong <sla...@gmail.com>
> > ---
> > arch/x86/kernel/cpu/mcheck/mce_amd.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c
> > b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> > index 5d4999f..f727701 100644
> > --- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
> > +++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> > @@ -253,9 +253,10 @@ void mce_amd_feature_init(struct cpuinfo_x86 *c)
> > }
> >
> > mce_threshold_block_init(&b, offset);
> > - mce_threshold_vector = amd_threshold_interrupt;
> > }
> > }
> > +
> > + mce_threshold_vector = amd_threshold_interrupt;
>
> Looking at this more, it is theoretically possible that we break out
> of the both loops without *any* thresholding registers detected and to
> still assign a thresholding interrupt vector which would be clearly
> wrong.
Yes! In this case, mce_threshold_vector should be `default_threshold_interrupt'
rather than
amd_threshold_interrupt.
> Thus I think something like below should be much safer (I tried it with
> a label and goto already but it is uglier):
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c
> b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> index 9ce64955559d..9af7bd74828b 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> @@ -253,7 +253,9 @@ void mce_amd_feature_init(struct cpuinfo_x86 *c)
> }
>
> mce_threshold_block_init(&b, offset);
> - mce_threshold_vector = amd_threshold_interrupt;
> +
> + if (mce_threshold_vector != amd_threshold_interrupt)
> + mce_threshold_vector = amd_threshold_interrupt;
Perhaps the above assignment operation should be put into
if (b.interrupt_capable) {
... ...
if (mce_threshold_vector != amd_threshold_interrupt)
mce_threshold_vector = amd_threshold_interrupt;
}
If IntP (Thresholding Interrupt Supported) bit is zero, this indicates that the
reporting
of threshold overflow via interrupt isn't supported. So there's no need to
execute the
above assignment operation.
> }
> }
> }
>
> Looking at the asm, we still go and fetch those addresses so not really
> a win:
>
> cmpq $amd_threshold_interrupt, mce_threshold_vector(%rip) #,
> mce_threshold_vector
> je .L235 #,
> incl %r13d # block
> movq $amd_threshold_interrupt, mce_threshold_vector(%rip) #,
> mce_threshold_vector
> cmpl $9, %r13d #, block
>
> but this way the code is relatively clean. Unless you can come up with
> a nicer, cleaner version to handle the breaking out in the success and
> failure case...
Seems like I don't have any better idea than this.
thx!
cyc
From: Chen Yucong <sla...@gmail.com>
Subject: [PATCH] x86, MCE, AMD: avoid inappropriate assignment operation in
mce_amd_feature_init
Before executing "mce_threshold_vector = amd_threshold_interrupt;", a few
conditions should be checked for avoiding inappropriate assignment operations,
for example, IntP (Thresholding Interrupt Supported) bit of MCx_MISCi.
Signed-off-by: Chen Yucong <sla...@gmail.com>
---
arch/x86/kernel/cpu/mcheck/mce_amd.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c
b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 5d4999f..31bf792 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -250,10 +250,13 @@ void mce_amd_feature_init(struct cpuinfo_x86 *c)
if (b.interrupt_capable) {
int new = (high & MASK_LVTOFF_HI) >> 20;
offset = setup_APIC_mce(offset, new);
+
+ if (offset == new &&
+ mce_threshold_vector !=
amd_threshold_interrupt)
+ mce_threshold_vector =
amd_threshold_interrupt;
}
mce_threshold_block_init(&b, offset);
- mce_threshold_vector = amd_threshold_interrupt;
}
}
}
--
1.7.10.4
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