From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
david.kaplan@amd.com, mst@redhat.com, f.hetzelt@tu-berlin.de,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
konrad.wilk@oracle.com, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [PATCH 7/9] virtio-pci: harden INTX interrupts
Date: Tue, 14 Sep 2021 13:09:31 +0200 [thread overview]
Message-ID: <87tuinct1w.ffs@tglx> (raw)
In-Reply-To: <YUCBZjjk77q8JS4f@hirez.programming.kicks-ass.net>
On Tue, Sep 14 2021 at 13:03, Peter Zijlstra wrote:
> On Mon, Sep 13, 2021 at 11:36:24PM +0200, Thomas Gleixner wrote:
> Here you rely on the UNLOCK+LOCK pattern because we have two adjacent
> critical sections (or rather, the same twice), which provides RCtso
> ordering, which is sufficient to make the below store:
>
>>
>> intx_soft_enabled = true;
>
> a RELEASE. still, I would suggest writing it at least using
> WRITE_ONCE() with a comment on.
Right. forgot about that.
> disable_irq();
> /*
> * The above disable_irq() provides TSO ordering and as such
> * promotes the below store to store-release.
> */
> WRITE_ONCE(intx_soft_enabled, true);
> enable_irq();
>
>> In this case synchronize_irq() prevents the subsequent store to
>> intx_soft_enabled to leak into the __disable_irq(desc) section which in
>> turn makes it impossible for an interrupt handler to observe
>> intx_soft_enabled == true before the prerequisites which preceed the
>> call to disable_irq() are visible.
>>
>> Of course the memory ordering wizards might disagree, but if they do,
>> then we have a massive chase of ordering problems vs. similar constructs
>> all over the tree ahead of us.
>
> Your case, UNLOCK s + LOCK s, is fully documented to provide RCtso
> ordering. The more general case of: UNLOCK r + LOCK s, will shortly
> appear in documentation near you. Meaning we can forget about the
> details an blanket state that any UNLOCK followed by a LOCK (on the same
> CPU) will provide TSO ordering.
I think we also should document the disable/synchronize_irq() scheme
somewhere.
Thanks,
tglx
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next prev parent reply other threads:[~2021-09-14 11:09 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 5:53 [PATCH 0/9] More virtio hardening Jason Wang
2021-09-13 5:53 ` [PATCH 1/9] virtio-blk: validate num_queues during probe Jason Wang
2021-09-13 7:48 ` Stefano Garzarella
2021-09-14 2:29 ` Jason Wang
2021-09-13 12:05 ` Stefan Hajnoczi
2021-09-13 5:53 ` [PATCH 2/9] virtio: add doc for validate() method Jason Wang
2021-09-13 5:53 ` [PATCH 3/9] virtio-console: switch to use .validate() Jason Wang
2021-09-13 5:53 ` [PATCH 4/9] virtio_console: validate max_nr_ports before trying to use it Jason Wang
2021-09-13 5:53 ` [PATCH 5/9] virtio_config: introduce a new ready method Jason Wang
2021-09-13 5:53 ` [PATCH 6/9] virtio_pci: harden MSI-X interrupts Jason Wang
2021-09-13 6:03 ` Michael S. Tsirkin
2021-09-13 6:08 ` Jason Wang
2021-09-13 6:28 ` Michael S. Tsirkin
2021-09-13 6:34 ` Jason Wang
2021-09-13 6:37 ` Michael S. Tsirkin
2021-09-13 6:43 ` Jason Wang
2021-09-13 7:01 ` Michael S. Tsirkin
2021-09-13 7:15 ` Jason Wang
2021-09-13 6:50 ` Michael S. Tsirkin
2021-09-13 7:07 ` Jason Wang
2021-09-13 19:38 ` Thomas Gleixner
2021-09-13 20:54 ` Michael S. Tsirkin
2021-09-13 22:31 ` Thomas Gleixner
2021-09-14 2:20 ` Jason Wang
2021-09-14 8:29 ` Thomas Gleixner
2021-09-13 5:53 ` [PATCH 7/9] virtio-pci: harden INTX interrupts Jason Wang
2021-09-13 6:33 ` Michael S. Tsirkin
2021-09-13 6:36 ` Jason Wang
2021-09-13 6:41 ` Michael S. Tsirkin
2021-09-13 6:45 ` Jason Wang
2021-09-13 7:02 ` Michael S. Tsirkin
2021-09-13 7:17 ` Jason Wang
2021-09-13 21:36 ` Thomas Gleixner
2021-09-13 22:01 ` Michael S. Tsirkin
2021-09-13 22:20 ` Thomas Gleixner
2021-09-14 2:50 ` Jason Wang
2021-09-14 9:34 ` Boqun Feng
2021-09-14 11:03 ` Peter Zijlstra
2021-09-14 11:09 ` Thomas Gleixner [this message]
2021-09-13 5:53 ` [PATCH 8/9] virtio_ring: fix typos in vring_desc_extra Jason Wang
2021-09-13 5:53 ` [PATCH 9/9] virtio_ring: validate used buffer length Jason Wang
2021-09-13 6:36 ` Michael S. Tsirkin
2021-09-13 6:40 ` Jason Wang
2021-09-13 6:57 ` Michael S. Tsirkin
2021-09-13 7:13 ` Jason Wang
2021-10-05 7:42 ` [PATCH 0/9] More virtio hardening Michael S. Tsirkin
2021-10-11 7:36 ` Jason Wang
2021-10-11 12:36 ` Michael S. Tsirkin
2021-10-12 2:43 ` Jason Wang
2021-10-12 5:44 ` Michael S. Tsirkin
2021-10-12 6:11 ` Jason Wang
2021-10-12 6:35 ` Michael S. Tsirkin
2021-10-12 6:43 ` Jason Wang
2021-10-12 7:03 ` Michael S. Tsirkin
2021-10-12 8:46 ` Jason Wang
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