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

[Thomas Huth]

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.

> +    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.

> +    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).

> +    cnt->users--;
> +    if (cnt->users == 0) {
> +        QTAILQ_REMOVE(&s->zpci_dma_limit, cnt, link);
> +    }
> +}
> +
>  static void s390_pcihost_realize(DeviceState *dev, Error **errp)
>  {
>      PCIBus *b;
> @@ -764,6 +845,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error 
> **errp)
>      s->bus_no = 0;
>      QTAILQ_INIT(&s->pending_sei);
>      QTAILQ_INIT(&s->zpci_devs);
> +    QTAILQ_INIT(&s->zpci_dma_limit);
>  
>      css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false,
>                               S390_ADAPTER_SUPPRESSIBLE, errp);
> @@ -902,6 +984,7 @@ static void s390_pcihost_plug(HotplugHandler 
> *hotplug_dev, DeviceState *dev,
>  {
>      S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev);
>      PCIDevice *pdev = NULL;
> +    VFIOPCIDevice *vpdev = NULL;
>      S390PCIBusDevice *pbdev = NULL;
>  
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
> @@ -941,17 +1024,20 @@ static void s390_pcihost_plug(HotplugHandler 
> *hotplug_dev, DeviceState *dev,
>              }
>          }
>  
> +        pbdev->pdev = pdev;
> +        pbdev->iommu = s390_pci_get_iommu(s, pci_get_bus(pdev), pdev->devfn);
> +        pbdev->iommu->pbdev = pbdev;
> +        pbdev->state = ZPCI_FS_DISABLED;
> +
>          if (object_dynamic_cast(OBJECT(dev), "vfio-pci")) {
>              pbdev->fh |= FH_SHM_VFIO;
> +            vpdev = container_of(pbdev->pdev, VFIOPCIDevice, pdev);
> +            pbdev->iommu->dma_limit = s390_start_dma_count(s,
> +                                                           &vpdev->vbasedev);
>          } else {
>              pbdev->fh |= FH_SHM_EMUL;
>          }
>  
> -        pbdev->pdev = pdev;
> -        pbdev->iommu = s390_pci_get_iommu(s, pci_get_bus(pdev), pdev->devfn);
> -        pbdev->iommu->pbdev = pbdev;
> -        pbdev->state = ZPCI_FS_DISABLED;
> -
>          if (s390_pci_msix_init(pbdev)) {
>              error_setg(errp, "MSI-X support is mandatory "
>                         "in the S390 architecture");
> @@ -1004,6 +1090,9 @@ static void s390_pcihost_unplug(HotplugHandler 
> *hotplug_dev, DeviceState *dev,
>          pbdev->fid = 0;
>          QTAILQ_REMOVE(&s->zpci_devs, pbdev, link);
>          g_hash_table_remove(s->zpci_table, &pbdev->idx);
> +        if (pbdev->iommu->dma_limit) {
> +            s390_end_dma_count(s, pbdev->iommu->dma_limit);
> +        }
>          qdev_unrealize(dev);
>      }
>  }

 Thomas