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From: Nadav Amit <namit@vmware.com>
To: Andy Lutomirski <luto@kernel.org>,
	"Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"Metzger, Markus T" <markus.t.metzger@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro
Date: Fri, 26 Oct 2018 00:59:40 +0000	[thread overview]
Message-ID: <DFC98A15-9C61-4087-8F49-C9950A2D28F9@vmware.com> (raw)
In-Reply-To: <CALCETrV-fmLpwsa7tXZ8J+G5PQ6s0yhYVhY3jtE=FP9gAXc+QQ@mail.gmail.com>

From: Andy Lutomirski
Sent: October 26, 2018 at 12:25:17 AM GMT
> To: Bae, Chang Seok <chang.seok.bae@intel.com>, Nadav Amit <namit@vmware.com>
> Cc: Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Andrew Lutomirski <luto@kernel.org>, H. Peter Anvin <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, Metzger, Markus T <markus.t.metzger@intel.com>, Ravi V. Shankar <ravi.v.shankar@intel.com>, LKML <linux-kernel@vger.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@intel.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@zytor.com>
>> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
>> Cc: Andi Kleen <ak@linux.intel.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Dave Hansen <dave.hansen@linux.intel.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Ingo Molnar <mingo@kernel.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.


  reply	other threads:[~2018-10-26  0:59 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 18:42 [v3 00/12] x86: Enable FSGSBASE instructions Chang S. Bae
2018-10-23 18:42 ` [v3 01/12] taint: Introduce a new taint flag (insecure) Chang S. Bae
2018-10-24 18:50   ` Andy Lutomirski
2018-10-23 18:42 ` [v3 02/12] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2018-10-24 18:51   ` Andy Lutomirski
2018-10-23 18:42 ` [v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions Chang S. Bae
2018-10-24 18:53   ` Andy Lutomirski
2018-10-24 19:21     ` Andi Kleen
2018-10-25 23:14       ` Andy Lutomirski
2018-10-25 23:31         ` Linus Torvalds
2018-10-26  0:09           ` Andy Lutomirski
2018-10-23 18:42 ` [v3 04/12] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2018-10-24 19:16   ` Andy Lutomirski
2018-10-24 19:41     ` [Xen-devel] " Andrew Cooper
2018-10-25  6:09       ` Juergen Gross
2018-10-25 23:08         ` Andrew Cooper
2018-10-25 23:11           ` Andy Lutomirski
2018-10-25 23:14             ` Andrew Cooper
2018-10-25  7:32     ` Bae, Chang Seok
2018-10-25 23:00       ` Andy Lutomirski
2018-10-25 23:03         ` Bae, Chang Seok
2018-10-25 23:16     ` Andy Lutomirski
2018-10-23 18:42 ` [v3 05/12] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2018-10-24 19:21   ` Andy Lutomirski
2018-10-24 19:36     ` Bae, Chang Seok
2018-10-23 18:42 ` [v3 06/12] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions if available Chang S. Bae
2018-10-23 18:42 ` [v3 07/12] x86/fsgsbase/64: Introduce the new FIND_PERCPU_BASE macro Chang S. Bae
2018-10-26  0:25   ` Andy Lutomirski
2018-10-26  0:59     ` Nadav Amit [this message]
2018-10-23 18:42 ` [v3 08/12] x86/fsgsbase/64: Use the per-CPU base as GSBASE at the paranoid_entry Chang S. Bae
2018-10-23 18:42 ` [v3 09/12] selftests/x86/fsgsbase: Test WRGSBASE Chang S. Bae
2018-10-23 18:42 ` [v3 10/12] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2018-10-23 18:42 ` [v3 11/12] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2018-10-23 18:42 ` [v3 12/12] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae

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