On Tue, Jun 26, 2018 at 07:22:44PM +0100, Andrew Cooper wrote:
> One reoccuring code pattern is to read an MSR, modify one or more bits,
> and write the result back. Introduce helpers for this purpose.
>
> First, introduce rdmsr_split() and wrmsr_split() which are tiny static inline
> wrappers which deal with the MSR value in two 32bit halves.
>
> Next, construct msr_{set,clear}_bits() in terms of the {rdmsr,wrmsr}_split().
> The mask operations are deliberately performed as 32bit operations, because
> all callers pass in a constant to the mask parameter, and in all current
> cases, one of the two operations can be elided.
>
> For MSR_IA32_PSR_L3_QOS_CFG, switch PSR_L3_QOS_CDP_ENABLE from being a bit
> position variable to being a plain number.
>
> The resulting C is shorter, and doesn't require a temporary variable. The
> generated ASM is also more efficient, because of avoiding the
> packing/unpacking operations. e.g. the delta in the first hunk is from:
>
> b9 1b 00 00 00 mov $0x1b,%ecx
> 0f 32 rdmsr
> 48 c1 e2 20 shl $0x20,%rdx
> 48 09 d0 or %rdx,%rax
> 80 e4 f3 and $0xf3,%ah
> 48 89 c2 mov %rax,%rdx
> 48 c1 ea 20 shr $0x20,%rdx
> 0f 30 wrmsr
>
> to:
>
> b9 1b 00 00 00 mov $0x1b,%ecx
> 0f 32 rdmsr
> 80 e4 f3 and $0xf3,%ah
> 0f 30 wrmsr
>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Reviewed-by: Wei Liu <wei.l...@citrix.com>
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