Re: [PATCH] virtio-pci: correctly set virtio pci queue mem multiplier

["Michael S. Tsirkin" <mst@redhat.com>]

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 <schalla@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?

> ---
>  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