Re: [PATCH v2 06/20] nvme: add support for the abort command

[Klaus Birkelund <its@irrelevant.dk>]

On Fri, Nov 15, 2019 at 11:56:00AM +0000, Beata Michalska wrote:
> Hi Klaus,
> 
> On Wed, 13 Nov 2019 at 06:12, Klaus Birkelund <its@irrelevant.dk> wrote:
> >
> > On Tue, Nov 12, 2019 at 03:04:38PM +0000, Beata Michalska wrote:
> > > Hi Klaus
> > >
> >
> > Hi Beata,
> >
> > Thank you very much for your thorough reviews! I'll start going through
> > them one by one :) You might have seen that I've posted a v3, but I will
> > make sure to consolidate between v2 and v3!
> >
> > > On Tue, 15 Oct 2019 at 11:41, Klaus Jensen <its@irrelevant.dk> wrote:
> > > >
> > > > Required for compliance with NVMe revision 1.2.1. See NVM Express 1.2.1,
> > > > Section 5.1 ("Abort command").
> > > >
> > > > The Abort command is a best effort command; for now, the device always
> > > > fails to abort the given command.
> > > >
> > > > Signed-off-by: Klaus Jensen <klaus.jensen@cnexlabs.com>
> > > > ---
> > > >  hw/block/nvme.c | 16 ++++++++++++++++
> > > >  1 file changed, 16 insertions(+)
> > > >
> > > > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > > > index daa2367b0863..84e4f2ea7a15 100644
> > > > --- a/hw/block/nvme.c
> > > > +++ b/hw/block/nvme.c
> > > > @@ -741,6 +741,18 @@ static uint16_t nvme_identify(NvmeCtrl *n, NvmeCmd *cmd)
> > > >      }
> > > >  }
> > > >
> > > > +static uint16_t nvme_abort(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
> > > > +{
> > > > +    uint16_t sqid = le32_to_cpu(cmd->cdw10) & 0xffff;
> > > > +
> > > > +    req->cqe.result = 1;
> > > > +    if (nvme_check_sqid(n, sqid)) {
> > > > +        return NVME_INVALID_FIELD | NVME_DNR;
> > > > +    }
> > > > +
> > > Shouldn't we validate the CID as well ?
> > >
> >
> > According to the specification it is "implementation specific if/when a
> > controller chooses to complete the command when the command to abort is
> > not found".
> >
> > I'm interpreting this to mean that, yes, an invalid command identifier
> > could be given in the command, but this implementation does not care
> > about that.
> >
> > I still think the controller should check the validity of the submission
> > queue identifier though. It is a general invariant that the sqid should
> > be valid.
> >
> > > > +    return NVME_SUCCESS;
> > > > +}
> > > > +
> > > >  static inline void nvme_set_timestamp(NvmeCtrl *n, uint64_t ts)
> > > >  {
> > > >      trace_nvme_setfeat_timestamp(ts);
> > > > @@ -859,6 +871,7 @@ static uint16_t nvme_set_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
> > > >          trace_nvme_err_invalid_setfeat(dw10);
> > > >          return NVME_INVALID_FIELD | NVME_DNR;
> > > >      }
> > > > +
> > > >      return NVME_SUCCESS;
> > > >  }
> > > >
> > > > @@ -875,6 +888,8 @@ static uint16_t nvme_admin_cmd(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
> > > >          return nvme_create_cq(n, cmd);
> > > >      case NVME_ADM_CMD_IDENTIFY:
> > > >          return nvme_identify(n, cmd);
> > > > +    case NVME_ADM_CMD_ABORT:
> > > > +        return nvme_abort(n, cmd, req);
> > > >      case NVME_ADM_CMD_SET_FEATURES:
> > > >          return nvme_set_feature(n, cmd, req);
> > > >      case NVME_ADM_CMD_GET_FEATURES:
> > > > @@ -1388,6 +1403,7 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
> > > >      id->ieee[2] = 0xb3;
> > > >      id->ver = cpu_to_le32(0x00010201);
> > > >      id->oacs = cpu_to_le16(0);
> > > > +    id->acl = 3;
> > > So we are setting the max number of concurrent commands
> > > but there is no logic to enforce that and wrap up with the
> > > status suggested by specification.
> > >
> >
> > That is true, but because the controller always completes the Abort
> > command immediately this cannot happen. If the controller did try to
> > abort executing commands, the Abort command would need to linger in the
> > controller state until a completion queue entry is posted for the
> > command to be aborted before the completion queue entry can be posted
> > for the Abort command. This takes up resources in the controller and is
> > the reason for the Abort Command Limit.
> >
> > You could argue that we should set ACL to 0 then, but the specification
> > recommends a value of 3 and I do not see any harm in conveying a
> > "reasonable", though inconsequential, value.
> 
> Could we  potentially add some comment describing the above ?
> 

Yes, absolutely! :)


Klaus