linux-kernel - Re: [PATCH 5/9] x86/uv: Use the right tlbflush API

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Date:   Tue, 5 Dec 2017 17:04:44 -0600
From:   Andrew Banman <abanman@....com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>, <keescook@...gle.com>,
        <hughd@...gle.com>, Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        <daniel.gruss@...k.tugraz.at>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>, <moritz.lipp@...k.tugraz.at>,
        <linux-mm@...ck.org>, Borislav Petkov <bp@...en8.de>,
        <michael.schwarz@...k.tugraz.at>,
        <richard.fellner@...dent.tugraz.at>,
        Mike Travis <mike.travis@....com>
Subject: Re: [PATCH 5/9] x86/uv: Use the right tlbflush API



On 12/5/17 3:27 PM, Peter Zijlstra wrote:
> On Tue, Dec 05, 2017 at 03:09:48PM -0600, Andrew Banman wrote:
>> On 12/5/17 6:34 AM, Peter Zijlstra wrote:
>>> Since uv_flush_tlb_others() implements flush_tlb_others() which is
>>> about flushing user mappings, we should use __flush_tlb_single(),
>>> which too is about flushing user mappings.
>>>
>>> Cc: Andrew Banman<abanman@....com>
>>> Cc: Mike Travis<mike.travis@....com>
>>> Signed-off-by: Peter Zijlstra (Intel)<peterz@...radead.org>
>>> ---
>>>   arch/x86/platform/uv/tlb_uv.c |    2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> --- a/arch/x86/platform/uv/tlb_uv.c
>>> +++ b/arch/x86/platform/uv/tlb_uv.c
>>> @@ -299,7 +299,7 @@ static void bau_process_message(struct m
>>>   		local_flush_tlb();
>>>   		stat->d_alltlb++;
>>>   	} else {
>>> -		__flush_tlb_one(msg->address);
>>> +		__flush_tlb_single(msg->address);
>>>   		stat->d_onetlb++;
>>>   	}
>>>   	stat->d_requestee++;
>>
>> This looks like the right thing to do. We'll be testing it and complain later if
>> we find any problems, but I'm not expecting any since this patch looks to
>> maintain our status quo.
> 
> Well, with KPTI (the-patch-set-formerly-known-as-kaiser), there will be
> a distinct difference between the two.
> 
> With KPTI __flush_tlb_one() would end up invalidating all kernel
> mappings while __flush_tlb_single() will end up only invalidating the
> user mappings of the current mm.
> 

Right! Now the KPTI __flush_tlb_single() equals the old
__flush_tlb_one(), less the call to count_vm_tlb_event().

ACK