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X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Kevin Wolf , Paolo Bonzini , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/5/19 3:47 AM, Maxim Levitsky wrote: > On Mon, 2019-06-03 at 18:25 -0400, John Snow wrote: >> >> On 4/17/19 3:53 PM, Maxim Levitsky wrote: >>> Phase bits are only set by the hardware to indicate new completions >>> and not by the device driver. >>> >>> Signed-off-by: Maxim Levitsky >>> --- >>> block/nvme.c | 2 -- >>> 1 file changed, 2 deletions(-) >>> >>> diff --git a/block/nvme.c b/block/nvme.c >>> index 0684bbd077..2d208000df 100644 >>> --- a/block/nvme.c >>> +++ b/block/nvme.c >>> @@ -340,8 +340,6 @@ static bool nvme_process_completion(BDRVNVMeState *s, NVMeQueuePair *q) >>> qemu_mutex_lock(&q->lock); >>> c->cid = cpu_to_le16(0); >>> q->inflight--; >>> - /* Flip Phase Tag bit. */ >>> - c->status = cpu_to_le16(le16_to_cpu(c->status) ^ 0x1); >>> progress = true; >>> } >>> if (progress) { >>> >> >> Since you've not got much traction on this and you've pinged a v2, can >> you point me to a spec or a reproducer that illustrates the problem? >> >> (Or wait for more NVME knowledgeable people to give you a review...!) > > "A Completion Queue entry is posted to the Completion Queue when the controller write of that Completion > Queue entry to the next free Completion Queue slot inverts the Phase Tag (P) bit from its previous value > in memory. The controller may generate an interrupt to the host to indicate that one or more Completion > Queue entries have been posted." > In the future, please reference the sections in your commit messages when relevant: NVM Express 1.3, Section 4.1 "Submission Queue & Completion Queue Definition" I also found 4.6 "Completion Queue Entry" to be informative; especially Figure 28 which defines the phase bit. So: This looks right; does this fix a bug that can be observed? Do we have any regression tests for block/NVMe? --js > > > Best regards, > Maxim Levitsky >