On Wed, 16 Sep 2020 08:55:00 -0400
Matthew Rosato <mjrosato@xxxxxxxxxxxxx> wrote:
> On 9/16/20 6:27 AM, Cornelia Huck wrote:
> > On Wed, 16 Sep 2020 09:21:39 +0200
> > Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> wrote:
> >
> >> On 9/15/20 9:14 PM, Matthew Rosato wrote:
> >>> Create new files for separating out vfio-specific work for s390
> >>> pci. Add the first such routine, which issues VFIO_IOMMU_GET_INFO
> >>> ioctl to collect the current dma available count.
> >>>
> >>> Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> >>> ---
> >>> hw/s390x/meson.build | 1 +
> >>> hw/s390x/s390-pci-vfio.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++
> >>> hw/s390x/s390-pci-vfio.h | 17 +++++++++++++++
> >>> 3 files changed, 72 insertions(+)
> >>> create mode 100644 hw/s390x/s390-pci-vfio.c
> >>> create mode 100644 hw/s390x/s390-pci-vfio.h
> >>>
> >
> > (...)
> >
> >>> diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
> >>> new file mode 100644
> >>> index 0000000..75e3ac1
> >>> --- /dev/null
> >>> +++ b/hw/s390x/s390-pci-vfio.c
> >>> @@ -0,0 +1,54 @@
> >>> +/*
> >>> + * s390 vfio-pci interfaces
> >>> + *
> >>> + * Copyright 2020 IBM Corp.
> >>> + * Author(s): Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> >>> + *
> >>> + * This work is licensed under the terms of the GNU GPL, version 2 or (at
> >>> + * your option) any later version. See the COPYING file in the top-level
> >>> + * directory.
> >>> + */
> >>> +
> >>> +#include <sys/ioctl.h>
> >>> +
> >>> +#include "qemu/osdep.h"
> >>> +#include "s390-pci-vfio.h"
> >>> +#include "hw/vfio/vfio-common.h"
> >>> +
> >>> +/*
> >>> + * Get the current DMA available count from vfio. Returns true if vfio is
> >>> + * limiting DMA requests, false otherwise. The current available count read
> >>> + * from vfio is returned in avail.
> >>> + */
> >>> +bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
> >>> +{
> >>> + g_autofree struct vfio_iommu_type1_info *info;
> >>> + uint32_t argsz;
> >>> + int ret;
> >>> +
> >>> + assert(avail);
> >>> +
> >>> + argsz = sizeof(struct vfio_iommu_type1_info);
> >>> + info = g_malloc0(argsz);
> >>> + info->argsz = argsz;
> >>> + /*
> >>> + * If the specified argsz is not large enough to contain all
> >>> + * capabilities it will be updated upon return. In this case
> >>> + * use the updated value to get the entire capability chain.
> >>> + */
> >>> + ret = ioctl(fd, VFIO_IOMMU_GET_INFO, info);
> >>> + if (argsz != info->argsz) {
> >>> + argsz = info->argsz;
> >>> + info = g_realloc(info, argsz);
> >>
> >> Do we need to bzero [sizeof(struct vfio_iommu_type1_info)..argsz[?
> >
> > If we do, I think we need to do the equivalent in
> > vfio_get_region_info() as well?
> >
>
> I agree that it would need to be in both places or neither -- I would
> expect the re-driven ioctl to overwrite the prior contents of info
> (unless we get a bad ret, but in this case we don't care what is in info)?
>
> Perhaps the fundamental difference between this code and
> vfio_get_region_info is that the latter checks for only a growing argsz
> and retries, whereas this code checks for != so it's technically
> possible for a smaller argsz to trigger the retry here, and we wouldn't
> know for sure that all bytes from the first ioctl call were overwritten.
Nod. Relying on overwriting should be fine.
>
> What if I adjust this code to look like vfio_get_region_info:
>
> retry:
> info->argsz = argsz;
>
> if (ioctl(fd, VFIO_IOMMU_GET_INFO, info)) {
> // no need to g_free() bc of g_autofree
> return false;
> }
>
> if (info->argsz > argsz) {
> argsz = info->argsz;
> info = g_realloc(info, argsz);
> goto retry;
> }
>
> /* If the capability exists, update with the current value */
> return vfio_get_info_dma_avail(info, avail);
>
> Now we would only trigger when we are told by the host that the buffer
> must be larger.
I think that makes sense.
>
> > (Also, shouldn't we check ret before looking at info->argsz?)
> >
>
> Yes, you are correct. The above proposal would fix that issue too.
>
> >>
> >>> + info->argsz = argsz;
> >>> + ret = ioctl(fd, VFIO_IOMMU_GET_INFO, info);
> >>> + }
> >>> +
> >>> + if (ret) {
> >>> + return false;
> >>> + }
> >>> +
> >>> + /* If the capability exists, update with the current value */
> >>> + return vfio_get_info_dma_avail(info, avail);
> >>> +}
> >>> +
> >
> > (...)
> >
> >
>
