linux-kernel - Re: [External] [PATCH RFC/RFT v2 3/4] riscv: Stop emitting preventive sfence.vma for new vmalloc mappings

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Date: Tue, 4 Jun 2024 09:51:55 +0100
From: Conor Dooley <conor@...nel.org>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: yunhui cui <cuiyunhui@...edance.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ved Shanbhogue <ved@...osinc.com>, Matt Evans <mev@...osinc.com>,
	Dylan Jhong <dylan@...estech.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [External] [PATCH RFC/RFT v2 3/4] riscv: Stop emitting
 preventive sfence.vma for new vmalloc mappings

On Tue, Jun 04, 2024 at 09:17:26AM +0200, Alexandre Ghiti wrote:
> On Tue, Jun 4, 2024 at 9:15 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
> > On Tue, Jun 4, 2024 at 8:21 AM yunhui cui <cuiyunhui@...edance.com> wrote:
> > >
> > > As for the current status of the patch, there are two points that can
> > > be optimized:
> > > 1. Some chip hardware implementations may not cache TLB invalid
> > > entries, so it doesn't matter whether svvptc is available or not. Can
> > > we consider adding a CONFIG_RISCV_SVVPTC to control it?
> 
> That would produce a non-portable kernel. But I'm not opposed to that
> at all, let me check how we handle other extensions. Maybe @Conor
> Dooley has some feedback here?

To be honest, not really sure what to give feedback on. Could you
elaborate on exactly what the option is going to do? Given the
portability concern, I guess you were proposing that the option would
remove the preventative fences, rather than your current patch that
removes them via an alternative? I don't think we have any extension
related options that work like that at the moment, and making that an
option will just mean that distros that look to cater for multiple
platforms won't be able to turn it on.

Thanks,
Conor.

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