Re: [PATCH v2 2/2] vfio/common: Add trace point when a MMIO RAM section less than PAGE_SIZE

[Kunkun Jiang]

Hi Eric,

On 2021/10/22 1:02, Eric Auger wrote:
> Hi Kunkun,
>
> On 9/14/21 3:53 AM, Kunkun Jiang wrote:
> > The MSI-X structures of some devices and other non-MSI-X structures
> > are in the same BAR. They may share one host page, especially in the
> may be in the same bar?
You are right. So embarrassing.😅
> > case of large page granularity, such as 64K.
> >
> > For example, MSIX-Table size of 82599 NIC is 0x30 and the offset in
> > Bar 3(size 64KB) is 0x0. If host page size is 64KB.
> remove the '.'
s/./, ?
> In that case wouldn't the symptom be the same with a 4kB page?
Host page size is different, iova is different.
> iova = REAL_HOST_PAGE_ALIGN(section->offset_within_address_space);

If host page size is 4KB, the iova will smaller than llend.
If host page size is 64KB, the iova will be equal to llend.

> > vfio_listener_region_add() will be called to map the remaining range
> > (0x30-0xffff). And it will return early at
> > 'int128_ge((int128_make64(iova), llend))' and hasn't any message.
> s/and hasn't any message /without any message

Ok, I will correct this in next version.

> > Let's add a trace point to informed users like commit 5c08600547c0
> s/informed/inform
Same for this.
> > ("vfio: Use a trace point when a RAM section cannot be DMA mapped")
> > did.
> >
> > Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> > ---
> >   hw/vfio/common.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index 8728d4d5c2..2fc6213c0f 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -892,6 +892,13 @@ static void vfio_listener_region_add(MemoryListener 
> > *listener,
> >       llend = int128_and(llend, int128_exts64(qemu_real_host_page_mask));
> >   
> >       if (int128_ge(int128_make64(iova), llend)) {
> > +        if (memory_region_is_ram_device(section->mr)) {
> > +            trace_vfio_listener_region_add_no_dma_map(
> > +                memory_region_name(section->mr),
> > +                section->offset_within_address_space,
> > +                int128_getlo(section->size),
> > +                qemu_real_host_page_size);
> > +        }
> >           return;
> >       }
> >       end = int128_get64(int128_sub(llend, int128_one()));
By the way, if this patch is accepted. The following code in the
vfio_listener_region_add may need to be deleted:
>     if (memory_region_is_ram_device(section->mr)) {
>         hwaddr pgmask = (1ULL << ctz64(hostwin->iova_pgsizes)) - 1;
>
>         if ((iova & pgmask) || (int128_get64(llsize) & pgmask)) {
>             trace_vfio_listener_region_add_no_dma_map(
>                 memory_region_name(section->mr),
>                 section->offset_within_address_space,
>                 int128_getlo(section->size),
>                 pgmask + 1);
>             return;
>         }
>     }
What do you think?

Thanks,
Kunkun Jiang
> Thanks
>
> Eric
>
> .