From: Oliver Upton <oliver.upton@linux.dev> To: Will Deacon <will@kernel.org> Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>, linux-kernel@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>, kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Marek Szyprowski <m.szyprowski@samsung.com> Subject: Re: [PATCH v3 2/2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Date: Thu, 17 Nov 2022 18:23:23 +0000 [thread overview] Message-ID: <Y3Z8G3aCuRzzoq5e@google.com> (raw) In-Reply-To: <20221117174951.GA2916@willie-the-truck> Hi Will, Thanks for having a look. 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())? I had really only intended these to indirect lock acquisition/release, so the error handling on the caller side feels weird: static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker) { if (WARN_ON(walker->flags & KVM_PGTABLE_WALK_SHARED)) return -EPERM; return 0; } r = kvm_pgtable_walk_begin() if (r) return r; r = _kvm_pgtable_walk(); kvm_pgtable_walk_end(); > Since you're rejigging things anyway, can you have this > function return int? If having this is a strong motivator I can do a v4. -- Thanks, Oliver _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
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: Thu, 17 Nov 2022 18:23:23 +0000 [thread overview] Message-ID: <Y3Z8G3aCuRzzoq5e@google.com> (raw) Message-ID: <20221117182323.si8h2-eVFah9Mt1Jfgd2ovaOaYlhsXz5TEtMR0j1E7I@z> (raw) In-Reply-To: <20221117174951.GA2916@willie-the-truck> Hi Will, Thanks for having a look. 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())? I had really only intended these to indirect lock acquisition/release, so the error handling on the caller side feels weird: static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker) { if (WARN_ON(walker->flags & KVM_PGTABLE_WALK_SHARED)) return -EPERM; return 0; } r = kvm_pgtable_walk_begin() if (r) return r; r = _kvm_pgtable_walk(); kvm_pgtable_walk_end(); > Since you're rejigging things anyway, can you have this > function return int? If having this is a strong motivator I can do a v4. -- Thanks, Oliver
next prev parent reply other threads:[~2022-11-17 18:23 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 [this message] 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 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=Y3Z8G3aCuRzzoq5e@google.com \ --to=oliver.upton@linux.dev \ --cc=catalin.marinas@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=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: linkBe 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).