linux-kernel - Re: [PATCH net-next] vhost: use "checked" versions of get_user() and put

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Message-ID: <CAHk-=whJ0T_0SMegsbssgtWgO85+nJPapn6B893JQkJ7x6K0Kw@mail.gmail.com>
Date: Fri, 14 Nov 2025 12:48:52 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Jon Kohler <jon@...anix.com>, Jason Wang <jasowang@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Eugenio Pérez <eperezma@...hat.com>, 
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, 
	Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH net-next] vhost: use "checked" versions of get_user() and put_user()

On Fri, 14 Nov 2025 at 11:09, David Laight <david.laight.linux@...il.com> wrote:
>
> I think that is currently only x86-64?
> There are patches in the pipeline for ppc.
> I don't think I've seen anything for arm32 or arm64.

Honestly, the fact that it's mainly true on x86-64 is simply because
that's the only architecture that has cared enough.

Pretty much everybody else is affected by the exact same speculation
bugs. Sometimes the speculation window might be so small that it
doesn't matter, but in most cases it's just that the architecture is
so irrelevant that it doesn't matter.

So no, this is not a "x86 only" issue. It might be a "only a couple of
architectures have cared enough for it to have any practical impact".

End result: if some other architecture still has a __get_user() that
is noticeably faster than get_user(), it's not an argument for keeping
__get_user() - it's an argument that that architecture likely isn't
very important.

           Linus