Re: [PATCH v2 2/3] s390x/pci: Honor DMA limits set by vfio

[Matthew Rosato]

On 9/15/20 8:54 AM, Thomas Huth wrote:
> On 15/09/2020 00.29, Matthew Rosato wrote:
> > When an s390 guest is using lazy unmapping, it can result in a very
> > large number of oustanding DMA requests, far beyond the default
> > limit configured for vfio.  Let's track DMA usage similar to vfio
> > in the host, and trigger the guest to flush their DMA mappings
> > before vfio runs out.
> >
> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> > ---
> >   hw/s390x/s390-pci-bus.c  | 99 +++++++++++++++++++++++++++++++++++++++++++++---
> >   hw/s390x/s390-pci-bus.h  |  9 +++++
> >   hw/s390x/s390-pci-inst.c | 29 +++++++++++---
> >   hw/s390x/s390-pci-inst.h |  3 ++
> >   4 files changed, 129 insertions(+), 11 deletions(-)
> >
> > diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> > index 92146a2..23474cd 100644
> > --- a/hw/s390x/s390-pci-bus.c
> > +++ b/hw/s390x/s390-pci-bus.c
> > @@ -11,6 +11,8 @@
> >    * directory.
> >    */
> >   
> > +#include <sys/ioctl.h>
> > +
> >   #include "qemu/osdep.h"
> >   #include "qapi/error.h"
> >   #include "qapi/visitor.h"
> > @@ -24,6 +26,9 @@
> >   #include "qemu/error-report.h"
> >   #include "qemu/module.h"
> >   
> > +#include "hw/vfio/pci.h"
> > +#include "hw/vfio/vfio-common.h"
> > +
> >   #ifndef DEBUG_S390PCI_BUS
> >   #define DEBUG_S390PCI_BUS  0
> >   #endif
> > @@ -737,6 +742,82 @@ static void s390_pci_iommu_free(S390pciState *s, PCIBus 
> > *bus, int32_t devfn)
> >       object_unref(OBJECT(iommu));
> >   }
> >   
> > +static bool s390_sync_dma_avail(int fd, unsigned int *avail)
> > +{
> > +    struct vfio_iommu_type1_info *info;
>
> You could use g_autofree to get rid of the g_free() at the end.

OK

> > +    uint32_t argsz;
> > +    bool rval = false;
> > +    int ret;
> > +
> > +    if (avail == NULL) {
> > +        return false;
> > +    }
>
> Since this is a "static" local function, and calling it with avail ==
> NULL does not make too much sense, I think I'd rather turn this into an
> assert() instead. >

Sure, sounds good.


> > +    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);
> > +        info->argsz = argsz;
> > +        ret = ioctl(fd, VFIO_IOMMU_GET_INFO, info);
> > +    }
> > +
> > +    if (ret) {
> > +        goto out;
> > +    }
> > +
> > +    /* If the capability exists, update with the current value */
> > +    rval = vfio_get_info_dma_avail(info, avail);
> > +
> > +out:
> > +    g_free(info);
> > +    return rval;
> > +}
> > +
> > +static S390PCIDMACount *s390_start_dma_count(S390pciState *s, VFIODevice *vdev)
> > +{
> > +    int id = vdev->group->container->fd;
> > +    S390PCIDMACount *cnt;
> > +    uint32_t avail;
> > +
> > +    if (!s390_sync_dma_avail(id, &avail)) {
> > +        return NULL;
> > +    }
> > +
> > +    QTAILQ_FOREACH(cnt, &s->zpci_dma_limit, link) {
> > +        if (cnt->id  == id) {
> > +            cnt->users++;
> > +            return cnt;
> > +        }
> > +    }
> > +
> > +    cnt = g_new0(S390PCIDMACount, 1);
> > +    cnt->id = id;
> > +    cnt->users = 1;
> > +    cnt->avail = avail;
> > +    QTAILQ_INSERT_TAIL(&s->zpci_dma_limit, cnt, link);
> > +    return cnt;
> > +}
> > +
> > +static void s390_end_dma_count(S390pciState *s, S390PCIDMACount *cnt)
> > +{
> > +    if (cnt == NULL) {
> > +        return;
> > +    }
>
> Either use assert() or drop this completely (since you're checking it at
> the caller site already).

Fair - I'll assert() here.  Thanks!