Re: [PATCH v6 01/20] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long

From: Borislav Petkov
Date: Thu Apr 04 2019 - 10:39:53 EST

On Wed, Apr 03, 2019 at 02:21:47PM -0700, Fenghua Yu wrote:
> cpu_caps_cleared and cpu_caps_set may not be aligned to unsigned long.
> Atomic operations (i.e. set_bit and clear_bit) on the bitmaps may access

Please end function names with parentheses.

> two cache lines (a.k.a. split lock) and lock the bus to block all memory

not "lock the bus" but "cause the CPU to do a bus lock... "

> accesses from other processors to ensure atomicity.
> To avoid the overall performance degradation from the bus locking, align
> the two variables to unsigned long.
> Defining the variables as unsigned long may also fix the issue because
> they are naturally aligned to unsigned long. But that needs additional
> code changes. Adding __aligned(unsigned long) is a simpler fix.
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> ---
> arch/x86/kernel/cpu/common.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)

With the above nitpicks addressed:

Reviewed-by: Borislav Petkov <bp@xxxxxxx>


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