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.
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.
(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);
+}
+
(...)
