On Thu, 2014-10-02 at 16:38 +0200, Borislav Petkov wrote:
>
> On Mon, Sep 22, 2014 at 09:11:00PM +0200, Borislav Petkov wrote:
> > On Mon, Sep 22, 2014 at 05:23:32PM +0800, Chen Yucong wrote:
> > > Hi Boris,
> > >
> > > I have found the following code snippet in mce_amd.c.
> > >
> > > /* cpu init entry point, called from mce.c with preempt off */
> > > void mce_amd_feature_init(struct cpuinfo_x86 *c)
> > > {
> > > ... ...
> > > for (bank = 0; bank < mca_cfg.banks; ++bank) {
> > > for (block = 0; block < NR_BLOCKS; ++block) {
> > > ... ...
> > > mce_threshold_block_init(&b, offset);
> > > mce_threshold_vector = amd_threshold_interrupt;
> > > }
> > > }
> > > }
> > >
> > > Why should "mce_threshold_vector = amd_threshold_interrupt" be placed in
> > > the inner loop body?
> >
> > Yeah, it was added sloppily with b276268631af3, I'm not surprised. Feel
> > free to send a fix.
>
> do you still want to send a fix or should I fix it up quickly?
>
From: Chen Yucong <[email protected]>
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 <[email protected]>
---
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;
}
/*
--
1.7.10.4
On Thu, Oct 02, 2014 at 11:20:12PM +0800, Chen Yucong wrote:
> From: Chen Yucong <[email protected]>
> 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 <[email protected]>
> ---
> 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.
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;
}
}
}
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...
Hmmm.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
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 <[email protected]>
> > 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 <[email protected]>
> > ---
> > 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 <[email protected]>
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 <[email protected]>
---
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