On 11.08.2025 08:36, Andrew Cooper wrote:
> On 08/08/2025 9:22 pm, Andrew Cooper wrote:
>> In hindsight, having the wrapper name not be the instruction mnemonic was a
>> poor choice. Also, PKS turns out to be quite rare in wanting a split value.
>>
>> Switch to using a single 64bit value in preparation for new users.
>>
>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
>> ---
>> CC: Jan Beulich <jbeul...@suse.com>
>> CC: Roger Pau Monné <roger....@citrix.com>
>> ---
>> xen/arch/x86/include/asm/msr.h | 4 ++--
>> xen/arch/x86/include/asm/prot-key.h | 4 ++--
>> 2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/xen/arch/x86/include/asm/msr.h b/xen/arch/x86/include/asm/msr.h
>> index 4c4f18b3a54d..b6b85b04c3fd 100644
>> --- a/xen/arch/x86/include/asm/msr.h
>> +++ b/xen/arch/x86/include/asm/msr.h
>> @@ -39,7 +39,7 @@ static inline void wrmsrl(unsigned int msr, uint64_t val)
>> }
>>
>> /* Non-serialising WRMSR, when available. Falls back to a serialising
>> WRMSR. */
>> -static inline void wrmsr_ns(uint32_t msr, uint32_t lo, uint32_t hi)
>> +static inline void wrmsrns(uint32_t msr, uint64_t val)
>> {
>> /*
>> * WRMSR is 2 bytes. WRMSRNS is 3 bytes. Pad WRMSR with a redundant CS
>> @@ -47,7 +47,7 @@ static inline void wrmsr_ns(uint32_t msr, uint32_t lo,
>> uint32_t hi)
>> */
>> alternative_input(".byte 0x2e; wrmsr",
>> ".byte 0x0f,0x01,0xc6", X86_FEATURE_WRMSRNS,
>> - "c" (msr), "a" (lo), "d" (hi));
>> + "c" (msr), "a" (val), "d" (val >> 32));
>> }
>
> It turns out this is the case poor code generation for MSR_STAR.
>
> I've adjusted it to:
>
> @@ -39,8 +39,10 @@ static inline void wrmsrl(unsigned int msr, uint64_t val)
> }
>
> /* Non-serialising WRMSR, when available. Falls back to a serialising
> WRMSR. */
> -static inline void wrmsr_ns(uint32_t msr, uint32_t lo, uint32_t hi)
> +static inline void wrmsrns(uint32_t msr, uint64_t val)
> {
> + uint32_t lo = val, hi = val >> 32;
> +
> /*
> * WRMSR is 2 bytes. WRMSRNS is 3 bytes. Pad WRMSR with a redundant CS
> * prefix to avoid a trailing NOP.
>
>
> which stops the compiler from loading the high half of %rax too.
Acked-by: Jan Beulich <jbeul...@suse.com>
