> -----Original Message-----
> From: Michael S. Tsirkin <m...@redhat.com>
> Sent: Tuesday, February 13, 2024 9:23 PM
> To: Srujana Challa <scha...@marvell.com>
> Cc: qemu-devel@nongnu.org; Vamsi Krishna Attunuru
> <vattun...@marvell.com>; Jerin Jacob <jer...@marvell.com>
> Subject: Re: [EXT] Re: [PATCH] virtio-pci: correctly set virtio pci queue mem
> multiplier
>
> On Tue, Feb 13, 2024 at 12:37:36PM +0000, Srujana Challa wrote:
> > > Subject: Re: [EXT] Re: [PATCH] virtio-pci: correctly set virtio pci
> > > queue mem multiplier
> > >
> > > On Tue, Feb 13, 2024 at 11:50:34AM +0000, Srujana Challa wrote:
> > > > > Subject: [EXT] Re: [PATCH] virtio-pci: correctly set virtio pci
> > > > > queue mem multiplier
> > > > >
> > > > > External Email
> > > > >
> > > > > ----------------------------------------------------------------
> > > > > ----
> > > > > -- On Mon, Feb 12, 2024 at 01:22:33PM +0530, Srujana Challa wrote:
> > > > > > Currently, virtio_pci_queue_mem_mult function returns 4K when
> > > > > > VIRTIO_PCI_FLAG_PAGE_PER_VQ is set. But this is not correct
> > > > > > when host has page size as 64K.
> > > > > > This patch fixes the same.
> > > > > >
> > > > > > Signed-off-by: Srujana Challa <scha...@marvell.com>
> > > > >
> > > > > You can't tweak guest visible values like this without compat
> > > > > machinery. It's also going to consume a ton more phys memory -
> > > > > can this
> > > break any configs?
> > > > > Why is this a problem? Just with vdpa?
> > > >
> > > > We are observing the issue with vdpa when host has page size of 64K.
> > > > We haven't verified any other backends. I think, any backend that
> > > > uses below API would fail if host has page size other than 4K right?
> > > > And also as per VIRTIO_PCI_FLAG_PAGE_PER_VQ, it should be equal to
> > > > page_size right?
> > > >
> > > > static int virtio_pci_set_host_notifier_mr(DeviceState *d, int n,
> > > > MemoryRegion *mr, bool
> > > > assign) {
> > > > VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
> > > > int offset;
> > > >
> > > > if (n >= VIRTIO_QUEUE_MAX || !virtio_pci_modern(proxy) ||
> > > > virtio_pci_queue_mem_mult(proxy) != memory_region_size(mr)) {
> > > > return -1;
> > > > }
> > >
> > > Yes but not everyone uses that right? Plain virtio in software with
> > > no tricks doesn't care?
> > Yes, any other better ways to address this issue.?
>
> Add a property that vdpa can set?
I think, as per VIRTIO_PCI_FLAG_PAGE_PER_VQ flag, it should be equal to
host Page_size. May be for software use, we can introduce one more flag, that
could be irrespective of host page_size?
>
>
> > >
> > >
> > > > >
> > > > > > ---
> > > > > > hw/virtio/virtio-pci.c | 4 +---
> > > > > > 1 file changed, 1 insertion(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> > > > > > index
> > > > > > e433879542..028df99991 100644
> > > > > > --- a/hw/virtio/virtio-pci.c
> > > > > > +++ b/hw/virtio/virtio-pci.c
> > > > > > @@ -316,12 +316,10 @@ static bool
> > > > > virtio_pci_ioeventfd_enabled(DeviceState *d)
> > > > > > return (proxy->flags & VIRTIO_PCI_FLAG_USE_IOEVENTFD) !=
> > > > > > 0; }
> > > > > >
> > > > > > -#define QEMU_VIRTIO_PCI_QUEUE_MEM_MULT 0x1000
> > > > > > -
> > > > > > static inline int virtio_pci_queue_mem_mult(struct
> > > > > > VirtIOPCIProxy
> > > > > > *proxy) {
> > > > > > return (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ) ?
> > > > > > - QEMU_VIRTIO_PCI_QUEUE_MEM_MULT : 4;
> > > > > > + qemu_real_host_page_size() : 4;
> > > > > > }
> > > > > >
> > > > > > static int virtio_pci_ioeventfd_assign(DeviceState *d,
> > > > > > EventNotifier *notifier,
> > > > > > --
> > > > > > 2.25.1
