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. ~Andrew