Re: [PATCH v2 02/12] hw/block/nvme: fix 64 bit register hi/lo split writes

[Minwoo Im <minwoo.im.dev@gmail.com>]

On 21-01-18 10:46:55, Klaus Jensen wrote:
> From: Klaus Jensen <k.jensen@samsung.com>
> 
> 64 bit registers like ASQ and ACQ should be writable by both a hi/lo 32
> bit write combination as well as a plain 64 bit write. The spec does not
> define ordering on the hi/lo split, but the code currently assumes that
> the low order bits are written first. Additionally, the code does not
> consider that another address might already have been written into the
> register, causing the OR'ing to result in a bad address.
> 
> Fix this by explicitly overwriting only the low or high order bits for
> 32 bit writes.
> 
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> ---
>  hw/block/nvme.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index bd7e258c3c26..40b9f8ccfc0e 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -3781,19 +3781,21 @@ static void nvme_write_bar(NvmeCtrl *n, hwaddr offset, uint64_t data,
>          trace_pci_nvme_mmio_aqattr(data & 0xffffffff);
>          break;
>      case 0x28:  /* ASQ */
> -        n->bar.asq = data;
> +        n->bar.asq = size == 8 ? data :
> +            (n->bar.asq & ~0xffffffff) | (data & 0xffffffff);
                             ^^^^^^^^^^^
If this one is to unmask lower 32bits other than higher 32bits, then
it should be:

	(n->bar.asq & ~0xffffffffULL)

Also, maybe we should take care of lower than 4bytes as:

	.min_access_size = 2,
	.max_access_size = 8,

Even we have some error messages up there with:

	if (unlikely(size < sizeof(uint32_t))) {
	    NVME_GUEST_ERR(pci_nvme_ub_mmiowr_toosmall,
			   "MMIO write smaller than 32-bits,"
			   " offset=0x%"PRIx64", size=%u",
			   offset, size);
	    /* should be ignored, fall through for now */
	}

It's a fall-thru error, and that's it.  I would prefer not to have this
error and support for 2bytes access also, OR do not support for 2bytes
access for this MMIO area.

Thanks!