linux-kernel - Re: [PATCH v2 8/9] x86/mm/tlb: Remove UV special case

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <6a40267d-f646-5406-db14-155ecd05cf48@hpe.com>
Date:   Tue, 9 Jul 2019 14:17:18 -0700
From:   Mike Travis <mike.travis@....com>
To:     Nadav Amit <namit@...are.com>
Cc:     Russ Anderson <rja@....com>, Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dimitri Sivanich <sivanich@....com>,
        Hedi Berriche <hedi.berriche@....com>
Subject: Re: [PATCH v2 8/9] x86/mm/tlb: Remove UV special case



On 7/9/2019 2:09 PM, Nadav Amit wrote:
>> On Jul 9, 2019, at 1:29 PM, Mike Travis <mike.travis@....com> wrote:
>>
>>
>>
>> On 7/9/2019 1:09 PM, Russ Anderson wrote:
>>> On Tue, Jul 09, 2019 at 09:50:27PM +0200, Thomas Gleixner wrote:
>>>> On Tue, 2 Jul 2019, Nadav Amit wrote:
>>>>
>>>>> SGI UV support is outdated and not maintained, and it is not clear how
>>>>> it performs relatively to non-UV. Remove the code to simplify the code.
>>>>
>>>> You should at least Cc the SGI/HP folks on that. They are still
>>>> around. Done so.
>>> Thanks Thomas.  The SGI UV is now HPE Superdome Flex and is
>>> very much still supported.
>>> Thanks.
>>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>>> Cc: Dave Hansen <dave.hansen@...el.com>
>>>>> Suggested-by: Andy Lutomirski <luto@...nel.org>
>>>>> Signed-off-by: Nadav Amit <namit@...are.com>
>>>>> ---
>>>>>   arch/x86/mm/tlb.c | 25 -------------------------
>>>>>   1 file changed, 25 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
>>>>> index b47a71820f35..64afe1215495 100644
>>>>> --- a/arch/x86/mm/tlb.c
>>>>> +++ b/arch/x86/mm/tlb.c
>>>>> @@ -689,31 +689,6 @@ void native_flush_tlb_multi(const struct cpumask *cpumask,
>>>>>   		trace_tlb_flush(TLB_REMOTE_SEND_IPI,
>>>>>   				(info->end - info->start) >> PAGE_SHIFT);
>>>>>   -	if (is_uv_system()) {
>>>>> -		/*
>>>>> -		 * This whole special case is confused.  UV has a "Broadcast
>>>>> -		 * Assist Unit", which seems to be a fancy way to send IPIs.
>>>>> -		 * Back when x86 used an explicit TLB flush IPI, UV was
>>>>> -		 * optimized to use its own mechanism.  These days, x86 uses
>>>>> -		 * smp_call_function_many(), but UV still uses a manual IPI,
>>>>> -		 * and that IPI's action is out of date -- it does a manual
>>>>> -		 * flush instead of calling flush_tlb_func_remote().  This
>>>>> -		 * means that the percpu tlb_gen variables won't be updated
>>>>> -		 * and we'll do pointless flushes on future context switches.
>>>>> -		 *
>>>>> -		 * Rather than hooking native_flush_tlb_multi() here, I think
>>>>> -		 * that UV should be updated so that smp_call_function_many(),
>>>>> -		 * etc, are optimal on UV.
>>>>> -		 */
>>
>> I thought this change was already proposed a bit ago and we acked it
>> awhile back. Also the replacement functionality is being worked on but it
>> is more complex. The smp call many has to support all the reasons why it’s
>> called and not just the tlb shoot downs as is the current BAU case.
> 
> Sorry for not cc’ing you before. In the meanwhile, can you give an explicit
> acked-by? (I couldn’t find the previous patch you regarded.)

Sure:

Acked-by: Mike Travis <mike.travis@....com>

> 
> Thanks,
> Nadav
>