From: Oliver Upton <oliver.upton@linux.dev>
To: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
kvmarm@lists.linux.dev,
Marek Szyprowski <m.szyprowski@samsung.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks
Date: Fri, 18 Nov 2022 17:12:49 +0000 [thread overview]
Message-ID: <Y3e9EXICIfgw4nSz@google.com> (raw)
Message-ID: <20221118171249.HZRBUeOHz5FdDXsMGomSDH0_qHFaB10V4a7C8iA7Ntk@z> (raw)
In-Reply-To: <20221118121949.GA3697@willie-the-truck>
On Fri, Nov 18, 2022 at 12:19:50PM +0000, Will Deacon wrote:
> On Thu, Nov 17, 2022 at 06:23:23PM +0000, Oliver Upton wrote:
> > On Thu, Nov 17, 2022 at 05:49:52PM +0000, Will Deacon wrote:
> > > On Wed, Nov 16, 2022 at 04:56:55PM +0000, Oliver Upton wrote:
> >
> > [...]
> >
> > > > -static inline void kvm_pgtable_walk_begin(void) {}
> > > > -static inline void kvm_pgtable_walk_end(void) {}
> > > > +static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
> > > > +{
> > > > + /*
> > > > + * Due to the lack of RCU (or a similar protection scheme), only
> > > > + * non-shared table walkers are allowed in the hypervisor.
> > > > + */
> > > > + WARN_ON(walker->flags & KVM_PGTABLE_WALK_SHARED);
> > > > +}
> > >
> > > I think it would be better to propagate the error to the caller rather
> > > than WARN here.
> >
> > I'd really like to warn somewhere though since we're rather fscked at
> > this point. Keeping that WARN close to the exceptional condition would
> > help w/ debugging.
> >
> > Were you envisioning bubbling the error all the way back up (i.e. early
> > return from kvm_pgtable_walk())?
>
> Yes, that's what I had in mind. WARN is fatal at EL2, so I think it's
> better to fail the pgtable operation rather than bring down the entire
> machine by default.
Duh, I forgot WARNs really do go boom at EL2. Yeah, in that case it'd be
best to let the caller clean up the mess.
> > If having this is a strong motivator I can do a v4.
>
> It's a really minor point, so I'll leave it up to you guys.
Sold (sorry I wasn't following before). v4 on the way.
--
Thanks,
Oliver
next prev parent reply other threads:[~2022-11-18 17:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-16 16:56 [PATCH v3 0/2] KVM: arm64: Fixes for parallel faults series Oliver Upton
2022-11-16 16:56 ` Oliver Upton
2022-11-16 16:56 ` [PATCH v3 1/2] KVM: arm64: Take a pointer to walker data in kvm_dereference_pteref() Oliver Upton
2022-11-16 16:56 ` Oliver Upton
2022-11-16 16:56 ` [PATCH v3 2/2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Oliver Upton
2022-11-16 16:56 ` Oliver Upton
2022-11-17 17:49 ` Will Deacon
2022-11-17 17:49 ` Will Deacon
2022-11-17 18:23 ` Oliver Upton
2022-11-17 18:23 ` Oliver Upton
2022-11-18 12:19 ` Will Deacon
2022-11-18 12:19 ` Will Deacon
2022-11-18 17:12 ` Oliver Upton [this message]
2022-11-18 17:12 ` Oliver Upton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y3e9EXICIfgw4nSz@google.com \
--to=oliver.upton@linux.dev \
--cc=alexandru.elisei@arm.com \
--cc=catalin.marinas@arm.com \
--cc=james.morse@arm.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=kvmarm@lists.linux.dev \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=m.szyprowski@samsung.com \
--cc=maz@kernel.org \
--cc=suzuki.poulose@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).