Re: [PATCH v1 2/4] x86/fred: Write to FRED MSRs with wrmsrns()
From: Peter Zijlstra
Date: Fri Jul 05 2024 - 05:28:37 EST
On Wed, Jul 03, 2024 at 05:00:53PM +0100, Andrew Cooper wrote:
> /* Non-serialising WRMSR, when available. Falls back to a serialising WRMSR. */
> static inline void wrmsrns(uint32_t msr, uint32_t lo, uint32_t hi)
> {
> /*
> * WRMSR is 2 bytes. WRMSRNS is 3 bytes. Pad WRMSR with a redundant CS
> * prefix to avoid a trailing NOP.
> */
> alternative_input(".byte 0x2e; wrmsr",
> ".byte 0x0f,0x01,0xc6", X86_FEATURE_WRMSRNS,
> "c" (msr), "a" (lo), "d" (hi));
> }
FWIW, I favour this variant.