From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: kvm@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
Will Deacon <will@kernel.org>,
kvmarm@lists.linux.dev, Ben Gardon <bgardon@google.com>,
David Matlack <dmatlack@google.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v5 08/14] KVM: arm64: Protect stage-2 traversal with RCU
Date: Wed, 9 Nov 2022 21:53:45 +0000 [thread overview]
Message-ID: <Y2whaWo3SIOOMKOE@google.com> (raw)
In-Reply-To: <20221107215644.1895162-9-oliver.upton@linux.dev>
On Mon, Nov 07, 2022, Oliver Upton wrote:
> Use RCU to safely walk the stage-2 page tables in parallel. Acquire and
> release the RCU read lock when traversing the page tables. Defer the
> freeing of table memory to an RCU callback. Indirect the calls into RCU
> and provide stubs for hypervisor code, as RCU is not available in such a
> context.
>
> The RCU protection doesn't amount to much at the moment, as readers are
> already protected by the read-write lock (all walkers that free table
> memory take the write lock). Nonetheless, a subsequent change will
> futher relax the locking requirements around the stage-2 MMU, thereby
> depending on RCU.
Two somewhat off-topic questions (because I'm curious):
1. Are there plans to enable "fast" page faults on ARM? E.g. to fixup access
faults (handle_access_fault()) and/or write-protection faults without acquiring
mmu_lock?
2. If the answer to (1) is "yes!", what's the plan to protect the lockless walks
for the RCU-less hypervisor code?
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WARNING: multiple messages have this Message-ID (diff)
From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
Reiji Watanabe <reijiw@google.com>,
Ricardo Koller <ricarkol@google.com>,
David Matlack <dmatlack@google.com>,
Quentin Perret <qperret@google.com>,
Ben Gardon <bgardon@google.com>, Gavin Shan <gshan@redhat.com>,
Peter Xu <peterx@redhat.com>, Will Deacon <will@kernel.org>,
kvmarm@lists.linux.dev
Subject: Re: [PATCH v5 08/14] KVM: arm64: Protect stage-2 traversal with RCU
Date: Wed, 9 Nov 2022 21:53:45 +0000 [thread overview]
Message-ID: <Y2whaWo3SIOOMKOE@google.com> (raw)
Message-ID: <20221109215345.Ed-rS_LJdikT4QJIAh6Pm_MIQ2XDmiOS-WLejjGxVqI@z> (raw)
In-Reply-To: <20221107215644.1895162-9-oliver.upton@linux.dev>
On Mon, Nov 07, 2022, Oliver Upton wrote:
> Use RCU to safely walk the stage-2 page tables in parallel. Acquire and
> release the RCU read lock when traversing the page tables. Defer the
> freeing of table memory to an RCU callback. Indirect the calls into RCU
> and provide stubs for hypervisor code, as RCU is not available in such a
> context.
>
> The RCU protection doesn't amount to much at the moment, as readers are
> already protected by the read-write lock (all walkers that free table
> memory take the write lock). Nonetheless, a subsequent change will
> futher relax the locking requirements around the stage-2 MMU, thereby
> depending on RCU.
Two somewhat off-topic questions (because I'm curious):
1. Are there plans to enable "fast" page faults on ARM? E.g. to fixup access
faults (handle_access_fault()) and/or write-protection faults without acquiring
mmu_lock?
2. If the answer to (1) is "yes!", what's the plan to protect the lockless walks
for the RCU-less hypervisor code?
next prev parent reply other threads:[~2022-11-09 21:53 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-07 21:56 [PATCH v5 00/14] KVM: arm64: Parallel stage-2 fault handling Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-07 21:56 ` [PATCH v5 01/14] KVM: arm64: Combine visitor arguments into a context structure Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:48 ` Oliver Upton
2022-11-09 22:48 ` Oliver Upton
2022-11-10 0:23 ` Gavin Shan
2022-11-10 0:23 ` Gavin Shan
2022-11-10 0:42 ` Oliver Upton
2022-11-10 0:42 ` Oliver Upton
2022-11-10 3:40 ` Gavin Shan
2022-11-10 3:40 ` Gavin Shan
2022-11-07 21:56 ` [PATCH v5 02/14] KVM: arm64: Stash observed pte value in visitor context Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-10 4:55 ` Gavin Shan
2022-11-10 4:55 ` Gavin Shan
2022-11-07 21:56 ` [PATCH v5 03/14] KVM: arm64: Pass mm_ops through the " Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-10 5:22 ` Gavin Shan
2022-11-10 5:22 ` Gavin Shan
2022-11-10 5:30 ` Gavin Shan
2022-11-10 5:30 ` Gavin Shan
2022-11-07 21:56 ` [PATCH v5 04/14] KVM: arm64: Don't pass kvm_pgtable through kvm_pgtable_walk_data Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-10 5:30 ` Gavin Shan
2022-11-10 5:30 ` Gavin Shan
2022-11-10 5:38 ` Oliver Upton
2022-11-10 5:38 ` Oliver Upton
2022-11-07 21:56 ` [PATCH v5 05/14] KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:54 ` Oliver Upton
2022-11-09 22:54 ` Oliver Upton
2022-11-07 21:56 ` [PATCH v5 06/14] KVM: arm64: Use an opaque type for pteps Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:23 ` Ben Gardon
2022-11-09 22:23 ` Ben Gardon
2022-11-07 21:56 ` [PATCH v5 07/14] KVM: arm64: Tear down unlinked stage-2 subtree after break-before-make Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:24 ` Ben Gardon
2022-11-09 22:24 ` Ben Gardon
2022-11-07 21:56 ` [PATCH v5 08/14] KVM: arm64: Protect stage-2 traversal with RCU Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 21:53 ` Sean Christopherson [this message]
2022-11-09 21:53 ` Sean Christopherson
2022-11-09 23:55 ` Oliver Upton
2022-11-09 23:55 ` Oliver Upton
2022-11-15 18:47 ` Ricardo Koller
2022-11-15 18:47 ` Ricardo Koller
2022-11-15 18:57 ` Oliver Upton
2022-11-15 18:57 ` Oliver Upton
2022-11-09 22:25 ` Ben Gardon
2022-11-09 22:25 ` Ben Gardon
2022-11-10 13:34 ` Marc Zyngier
2022-11-10 13:34 ` Marc Zyngier
2022-11-14 14:29 ` Marek Szyprowski
2022-11-14 14:29 ` Marek Szyprowski
2022-11-14 17:42 ` Oliver Upton
2022-11-14 17:42 ` Oliver Upton
2022-12-05 5:51 ` Mingwei Zhang
2022-12-05 5:51 ` Mingwei Zhang
2022-12-05 7:47 ` Oliver Upton
2022-12-05 7:47 ` Oliver Upton
2022-11-07 21:56 ` [PATCH v5 09/14] KVM: arm64: Atomically update stage 2 leaf attributes in parallel walks Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:26 ` Ben Gardon
2022-11-09 22:26 ` Ben Gardon
2022-11-09 22:42 ` Sean Christopherson
2022-11-09 22:42 ` Sean Christopherson
2022-11-09 23:00 ` Ben Gardon
2022-11-09 23:00 ` Ben Gardon
2022-11-10 13:40 ` Marc Zyngier
2022-11-10 13:40 ` Marc Zyngier
2022-11-07 21:56 ` [PATCH v5 10/14] KVM: arm64: Split init and set for table PTE Oliver Upton
2022-11-07 21:56 ` Oliver Upton
2022-11-09 22:26 ` Ben Gardon
2022-11-09 22:26 ` Ben Gardon
2022-11-09 23:00 ` Oliver Upton
2022-11-09 23:00 ` Oliver Upton
2022-11-07 21:58 ` [PATCH v5 11/14] KVM: arm64: Make block->table PTE changes parallel-aware Oliver Upton
2022-11-07 21:58 ` Oliver Upton
2022-11-09 22:26 ` Ben Gardon
2022-11-09 22:26 ` Ben Gardon
2022-11-09 23:03 ` Oliver Upton
2022-11-09 23:03 ` Oliver Upton
2022-11-07 21:59 ` [PATCH v5 12/14] KVM: arm64: Make leaf->leaf " Oliver Upton
2022-11-07 21:59 ` Oliver Upton
2022-11-09 22:26 ` Ben Gardon
2022-11-09 22:26 ` Ben Gardon
2022-11-07 22:00 ` [PATCH v5 13/14] KVM: arm64: Make table->block " Oliver Upton
2022-11-07 22:00 ` Oliver Upton
2022-11-07 22:00 ` [PATCH v5 14/14] KVM: arm64: Handle stage-2 faults in parallel Oliver Upton
2022-11-07 22:00 ` Oliver Upton
2022-11-11 15:47 ` [PATCH v5 00/14] KVM: arm64: Parallel stage-2 fault handling Marc Zyngier
2022-11-11 15:47 ` Marc Zyngier
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