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SubjectRe: [PATCH] nvmet-tcp: Don't kmap() pages which can't come from HIGHMEM
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>> @@ -329,7 +312,6 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd)
>> u32 length, offset, sg_offset;
>>
>> length = cmd->pdu_len;
>> - cmd->nr_mapped = DIV_ROUND_UP(length, PAGE_SIZE);
>> offset = cmd->rbytes_done;
>> cmd->sg_idx = offset / PAGE_SIZE;
>> sg_offset = offset % PAGE_SIZE;
>> @@ -338,7 +320,7 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd)
>> while (length) {
>> u32 iov_len = min_t(u32, length, sg->length - sg_offset);
>>
>> - iov->iov_base = kmap(sg_page(sg)) + sg->offset + sg_offset;
>> + iov->iov_base = page_address(sg_page(sg)) + sg->offset + sg_offset;
>> iov->iov_len = iov_len;
>>
>> length -= iov_len;
>> @@ -347,8 +329,7 @@ static void nvmet_tcp_map_pdu_iovec(struct nvmet_tcp_cmd *cmd)
>> sg_offset = 0;
>> }
>>
>> - iov_iter_kvec(&cmd->recv_msg.msg_iter, READ, cmd->iov,
>> - cmd->nr_mapped, cmd->pdu_len);
>> + iov_iter_kvec(&cmd->recv_msg.msg_iter, READ, cmd->iov, 0, cmd->pdu_len);
>> }
>
> I earlier meant just use a local variable for 'nr_mapped' rather than replace
> it with '0'. I don't think that 0 segments would result in usable kvec.

yes, that is wrong. Need a local int nr_mapped variable.

>
> I'm not even sure the existing code is correct, though. The sg->length can be
> higher order than a PAGE_SIZE, so it may be over-reporting nr_segs. It's just
> supposed to be the number of initialized iov's.

The sg is allocated with sgl_alloc so it is for sure 0-order.

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