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

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Message-ID: <20171205212727.GU3165@worktop.lehotels.local>
Date:   Tue, 5 Dec 2017 22:27:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Banman <abanman@....com>
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 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.