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

[Beata Michalska]

Hi Klaus,

On Wed, 13 Nov 2019 at 06:12, Klaus Birkelund <address@hidden> 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 <address@hidden> 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 <address@hidden>
> > > ---
> > >  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 ?

BR
Beata