On Mon, Apr 14, 2025 at 04:06:41PM +0200, Uros Bizjak wrote: > > > On 14. 04. 25 13:11, Peter Zijlstra wrote: > > What used to be a simple few instructions has turned into a giant mess > > (for x86_64). Not only does it use static_branch wrong, it mixes it > > with dynamic branches for no apparent reason. > > > > Notably it uses static_branch through an out-of-line function call, > > which completely defeats the purpose, since instead of a simple > > JMP/NOP site, you get a CALL+RET+TEST+Jcc sequence in return, which is > > absolutely idiotic. > > > > Add to that a dynamic test of hyperv_paravisor_present, something > > which is set once and never changed. > > > > Replace all this idiocy with a single direct function call to the > > right hypercall variant. > > > > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > > --- > > arch/x86/hyperv/hv_init.c | 21 ++++++ > > arch/x86/hyperv/ivm.c | 14 ++++ > > arch/x86/include/asm/mshyperv.h | 137 > > +++++++++++----------------------------- > > arch/x86/kernel/cpu/mshyperv.c | 18 +++-- > > 4 files changed, 88 insertions(+), 102 deletions(-) > > > > --- a/arch/x86/hyperv/hv_init.c > > +++ b/arch/x86/hyperv/hv_init.c > > @@ -35,7 +35,28 @@ > > #include <linux/highmem.h> > > void *hv_hypercall_pg; > > + > > +#ifdef CONFIG_X86_64 > > +u64 hv_pg_hypercall(u64 control, u64 param1, u64 param2) > > +{ > > + u64 hv_status; > > + > > + if (!hv_hypercall_pg) > > + return U64_MAX; > > + > > + register u64 __r8 asm("r8") = param2; > > + asm volatile (CALL_NOSPEC > > + : "=a" (hv_status), ASM_CALL_CONSTRAINT, > > + "+c" (control), "+d" (param1) > > + : "r" (__r8), > > r8 is call-clobbered register, so you should use "+r" (__r8) to properly > clobber it:
Ah, okay.
