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Date: Fri, 26 Oct 2018 00:59:40 +0000 From: Nadav Amit <namit@...are.com> To: Andy Lutomirski <luto@...nel.org>, "Bae, Chang Seok" <chang.seok.bae@...el.com> CC: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>, "Metzger, Markus T" <markus.t.metzger@...el.com>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro From: Andy Lutomirski Sent: October 26, 2018 at 12:25:17 AM GMT > To: Bae, Chang Seok <chang.seok.bae@...el.com>, Nadav Amit <namit@...are.com> > Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrew Lutomirski <luto@...nel.org>, H. Peter Anvin <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Metzger, Markus T <markus.t.metzger@...el.com>, Ravi V. Shankar <ravi.v.shankar@...el.com>, LKML <linux-kernel@...r.kernel.org> > 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 <chang.seok.bae@...el.com> 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 <hpa@...or.com> >> Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com> >> Cc: Andi Kleen <ak@...ux.intel.com> >> Cc: Andy Lutomirski <luto@...nel.org> >> Cc: Dave Hansen <dave.hansen@...ux.intel.com> >> Cc: Thomas Gleixner <tglx@...utronix.de> >> Cc: Ingo Molnar <mingo@...nel.org> >> --- >> 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.
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