Re: [PATCH v2 03/19] block/nvme: Introduce device/iommu 'page_size_min' variables

[Auger Eric]

Hi Philippe,

On 10/26/20 11:54 AM, Philippe Mathieu-Daudé wrote:
> Introduce device/iommu 'page_size_min' variables to make
> the code clearer.

I am unclear how much the device and the iommu page size must equal. For
instance, in [RFC 0/5] NVMe passthrough: Support 64kB page host, I have
a 64kB host page and an MPS set to 4kB.

Thanks

Eric
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  block/nvme.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/block/nvme.c b/block/nvme.c
> index aa290996679..5abd7257cac 100644
> --- a/block/nvme.c
> +++ b/block/nvme.c
> @@ -690,6 +690,8 @@ static int nvme_init(BlockDriverState *bs, const char 
> *device, int namespace,
>      uint64_t deadline, now;
>      Error *local_err = NULL;
>      volatile NvmeBar *regs = NULL;
> +    size_t device_page_size_min;
> +    size_t iommu_page_size_min = 4096;
>  
>      qemu_co_mutex_init(&s->dma_map_lock);
>      qemu_co_queue_init(&s->dma_flush_queue);
> @@ -724,7 +726,8 @@ static int nvme_init(BlockDriverState *bs, const char 
> *device, int namespace,
>          goto out;
>      }
>  
> -    s->page_size = MAX(4096, 1u << (12 + NVME_CAP_MPSMIN(cap)));
> +    device_page_size_min = 1u << (12 + NVME_CAP_MPSMIN(cap));
> +    s->page_size = MAX(iommu_page_size_min, device_page_size_min);
>      s->doorbell_scale = (4 << NVME_CAP_DSTRD(cap)) / sizeof(uint32_t);
>      bs->bl.opt_mem_alignment = s->page_size;
>      bs->bl.request_alignment = s->page_size;
>