Re: [PATCH v4 21/28] cxl/extent: Process DCD events and realize region extents

From: Ira Weiny
Date: Thu Oct 17 2024 - 17:18:19 EST

Jonathan Cameron wrote:
> On Wed, 9 Oct 2024 14:49:09 -0500
> Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
>
> > Li, Ming4 wrote:
> > > On 10/8/2024 7:16 AM, ira.weiny@xxxxxxxxx wrote:
> > > > From: Navneet Singh <navneet.singh@xxxxxxxxx>
> > > >

[snip]

> >
> > > > +static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
> > > > + struct xarray *extent_array, int cnt)
> > > > +{
> > > > + struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
> > > > + struct cxl_mbox_dc_response *p;
> > > > + struct cxl_mbox_cmd mbox_cmd;
> > > > + struct cxl_extent *extent;
> > > > + unsigned long index;
> > > > + u32 pl_index;
> > > > + int rc;
> > > > +
> > > > + size_t pl_size = struct_size(p, extent_list, cnt);
> > > > + u32 max_extents = cnt;
> > > > +
> > > > + /* May have to use more bit on response. */
> > > > + if (pl_size > cxl_mbox->payload_size) {
> > > > + max_extents = (cxl_mbox->payload_size - sizeof(*p)) /
> > > > + sizeof(struct updated_extent_list);
> > > > + pl_size = struct_size(p, extent_list, max_extents);
> > > > + }
> > > > +
> > > > + struct cxl_mbox_dc_response *response __free(kfree) =
> > > > + kzalloc(pl_size, GFP_KERNEL);
> > > > + if (!response)
> > > > + return -ENOMEM;
> > > > +
> > > > + pl_index = 0;
> > > > + xa_for_each(extent_array, index, extent) {
> > > > +
> > > > + response->extent_list[pl_index].dpa_start = extent->start_dpa;
> > > > + response->extent_list[pl_index].length = extent->length;
> > > > + pl_index++;
> > > > + response->extent_list_size = cpu_to_le32(pl_index);
> > > > +
> > > > + if (pl_index == max_extents) {
> > > > + mbox_cmd = (struct cxl_mbox_cmd) {
> > > > + .opcode = opcode,
> > > > + .size_in = struct_size(response, extent_list,
> > > > + pl_index),
> > > > + .payload_in = response,
> > > > + };
> > > > +
> > > > + response->flags = 0;
> > > > + if (pl_index < cnt)
> > > > + response->flags &= CXL_DCD_EVENT_MORE;
> > >
> > > It should be 'response->flags |= CXL_DCD_EVENT_MORE' here.
> >
> > Ah yea. Good catch.
> >
> > >
> > > Another issue is if 'cnt' is N times bigger than 'max_extents'(e,g. cnt=20, max_extents=10). all responses will be sent in this xa_for_each(), and CXL_DCD_EVENT_MORE will be set in the last response but it should not be set in these cases.
> > >
> >
> > Ah yes. cnt must be decremented. As I looked at the patch just now the
> >
> > if (cnt == 0 || pl_index)
> >
> > ... seemed very wrong to me. That change masked this bug.
> >
> > This should fix it:
> >
> > diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> > index d66beec687a0..99200274dea8 100644
> > --- a/drivers/cxl/core/mbox.c
> > +++ b/drivers/cxl/core/mbox.c
> > @@ -1119,10 +1119,11 @@ static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
> > if (rc)
> > return rc;
> > pl_index = 0;
> > + cnt -= pl_index;
> > }
> > }
> >
> > - if (cnt == 0 || pl_index) {
>
> I thought this cnt == 0 check was to deal with the no valid
> extents case where an empty reply is needed.

Yes but the bug found by Ming needs to be handled too. I see Fan is also
questioning this code.

So... for clarity among all of us here is the new function. I'm not thrilled
with the use of a goto but I think it is ok here.

Ira

static int cxl_send_dc_response(struct cxl_memdev_state *mds, int opcode,
struct xarray *extent_array, int cnt)
{
struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
struct cxl_mbox_dc_response *p;
struct cxl_mbox_cmd mbox_cmd;
struct cxl_extent *extent;
unsigned long index;
u32 pl_index;
int rc;

size_t pl_size = struct_size(p, extent_list, cnt);
u32 max_extents = cnt;

/* May have to use more bit on response. */
if (pl_size > cxl_mbox->payload_size) {
max_extents = (cxl_mbox->payload_size - sizeof(*p)) /
sizeof(struct updated_extent_list);
pl_size = struct_size(p, extent_list, max_extents);
}

struct cxl_mbox_dc_response *response __free(kfree) =
kzalloc(pl_size, GFP_KERNEL);
if (!response)
return -ENOMEM;

pl_index = 0;
if (cnt == 0)
goto send_zero_accepted;

xa_for_each(extent_array, index, extent) {
response->extent_list[pl_index].dpa_start = extent->start_dpa;
response->extent_list[pl_index].length = extent->length;
pl_index++;
response->extent_list_size = cpu_to_le32(pl_index);

if (pl_index == max_extents) {
mbox_cmd = (struct cxl_mbox_cmd) {
.opcode = opcode,
.size_in = struct_size(response, extent_list,
pl_index),
.payload_in = response,
};

response->flags = 0;
if (pl_index < cnt)
response->flags &= CXL_DCD_EVENT_MORE;

rc = cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);
if (rc)
return rc;
cnt -= pl_index;
pl_index = 0;
}
}

if (!pl_index)
return 0;

send_zero_accepted:
mbox_cmd = (struct cxl_mbox_cmd) {
.opcode = opcode,
.size_in = struct_size(response, extent_list,
pl_index),
.payload_in = response,
};

response->flags = 0;
return cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);
}