From: Andy Lutomirski Sent: October 26, 2018 at 12:25:17 AM GMT > To: Bae, Chang Seok <[email protected]>, Nadav Amit <[email protected]> > Cc: Ingo Molnar <[email protected]>, Thomas Gleixner <[email protected]>, > Andrew Lutomirski <[email protected]>, H. Peter Anvin <[email protected]>, Andi > Kleen <[email protected]>, Dave Hansen <[email protected]>, > Metzger, Markus T <[email protected]>, Ravi V. Shankar > <[email protected]>, LKML <[email protected]> > Subject: Re: [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE > macro > > > On Tue, Oct 23, 2018 at 11:43 AM Chang S. Bae <[email protected]> > wrote: >> GSBASE is used to find per-CPU data in the kernel. But when it is unknown, >> the per-CPU base can be found from the per_cpu_offset table with a CPU NR. >> The CPU NR is extracted from the limit field of the CPUNODE entry in GDT, >> or by the RDPID instruction. >> >> Also, add the GAS-compatible RDPID macro. >> >> The new macro will be used on a following patch. >> >> Suggested-by: H. Peter Anvin <[email protected]> >> Signed-off-by: Chang S. Bae <[email protected]> >> Cc: Andi Kleen <[email protected]> >> Cc: Andy Lutomirski <[email protected]> >> Cc: Dave Hansen <[email protected]> >> Cc: Thomas Gleixner <[email protected]> >> Cc: Ingo Molnar <[email protected]> >> --- >> arch/x86/include/asm/fsgsbase.h | 52 +++++++++++++++++++++++++++++++++ >> arch/x86/include/asm/inst.h | 15 ++++++++++ >> 2 files changed, 67 insertions(+) >> >> diff --git a/arch/x86/include/asm/fsgsbase.h >> b/arch/x86/include/asm/fsgsbase.h >> index e500d771155f..0c2d7d8a8c01 100644 >> --- a/arch/x86/include/asm/fsgsbase.h >> +++ b/arch/x86/include/asm/fsgsbase.h >> @@ -111,6 +111,58 @@ extern void x86_gsbase_write_cpu_inactive(unsigned long >> gsbase); >> MODRM 0xd0 wrgsbase_opd 1 >> .endm >> >> +#if CONFIG_SMP >> + >> +/* >> + * Fetch the per-CPU GSBASE value for this processor and put it in @reg. >> + * We normally use %gs for accessing per-CPU data, but we are setting up >> + * %gs here and obviously can not use %gs itself to access per-CPU data. >> + */ >> +.macro FIND_PERCPU_BASE_RDPID reg:req >> + /* >> + * The CPU/node NR is initialized earlier, directly in cpu_init(). > P >> + */ >> + RDPID \reg > > I would suggest that you instead add a macro LOAD_CPU_AND_NODE \reg > and have that macro contain the alternative. It can switch between > RDPID and LSL. This way you avoid duplicating the rest of it. > > This should end up in the same header as __getcpu() -- it probably > makes sense to just move __getcpu() for this purpose. > > Also, hpa and Nadav, shouldn't asm/inst.h end up in macros.S?
If there are going to be C uses, yes. Ingo was concerned that the .s file will be too big, so it should not be overly abused. In addition, I want to send a patch that recompiles all the .c files in macro.S changes. I’m worried it will start creating build problems.
