[PATCH v2 02/19] vfio: Convert to ram_block_discard_disable()

David Hildenbrand
2020-05-20T12:32:26Z

VFIO is (except devices without a physical IOMMU or some mediated devices)
incompatible with discarding of RAM. The kernel will pin basically all VM
memory. Let's convert to ram_block_discard_disable(), which can now
fail, in contrast to qemu_balloon_inhibit().

Leave "x-balloon-allowed" named as it is for now.

Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Pierre Morel <pmorel@linux.ibm.com>
Cc: Eric Farman <farman@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
hw/vfio/ap.c | 10 +++----
hw/vfio/ccw.c | 11 ++++----
hw/vfio/common.c | 53 +++++++++++++++++++----------------
hw/vfio/pci.c | 6 ++--
include/hw/vfio/vfio-common.h | 4 +--
5 files changed, 45 insertions(+), 39 deletions(-)

diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
index 95564c17ed..d0b1bc7581 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -105,12 +105,12 @@ static void vfio_ap_realize(DeviceState *dev, Error **errp)
vapdev->vdev.dev = dev;

/*
- * vfio-ap devices operate in a way compatible with
- * memory ballooning, as no pages are pinned in the host.
- * This needs to be set before vfio_get_device() for vfio common to
- * handle the balloon inhibitor.
+ * vfio-ap devices operate in a way compatible discarding of memory in
+ * RAM blocks, as no pages are pinned in the host. This needs to be
+ * set before vfio_get_device() for vfio common to handle
+ * ram_block_discard_disable().
*/
- vapdev->vdev.balloon_allowed = true;
+ vapdev->vdev.ram_block_discard_allowed = true;

ret = vfio_get_device(vfio_group, mdevid, &vapdev->vdev, errp);
if (ret) {
diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index c8624943c1..12dd44da52 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -425,12 +425,13 @@ static void vfio_ccw_get_device(VFIOGroup *group, VFIOCCWDevice *vcdev,

/*
* All vfio-ccw devices are believed to operate in a way compatible with
- * memory ballooning, ie. pages pinned in the host are in the current
- * working set of the guest driver and therefore never overlap with pages
- * available to the guest balloon driver. This needs to be set before
- * vfio_get_device() for vfio common to handle the balloon inhibitor.
+ * discarding of memory in RAM blocks, ie. pages pinned in the host are
+ * in the current working set of the guest driver and therefore never
+ * overlap e.g., with pages available to the guest balloon driver. This
+ * needs to be set before vfio_get_device() for vfio common to handle
+ * ram_block_discard_disable().
*/
- vcdev->vdev.balloon_allowed = true;
+ vcdev->vdev.ram_block_discard_allowed = true;

if (vfio_get_device(group, vcdev->cdev.mdevid, &vcdev->vdev, errp)) {
goto out_err;
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 0b3593b3c0..33357140b8 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -33,7 +33,6 @@
#include "qemu/error-report.h"
#include "qemu/main-loop.h"
#include "qemu/range.h"
-#include "sysemu/balloon.h"
#include "sysemu/kvm.h"
#include "sysemu/reset.h"
#include "trace.h"
@@ -1215,31 +1214,36 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
space = vfio_get_address_space(as);

/*
- * VFIO is currently incompatible with memory ballooning insofar as the
+ * VFIO is currently incompatible with discarding of RAM insofar as the
* madvise to purge (zap) the page from QEMU's address space does not
* interact with the memory API and therefore leaves stale virtual to
* physical mappings in the IOMMU if the page was previously pinned. We
- * therefore add a balloon inhibit for each group added to a container,
+ * therefore set discarding broken for each group added to a container,
* whether the container is used individually or shared. This provides
* us with options to allow devices within a group to opt-in and allow
- * ballooning, so long as it is done consistently for a group (for instance
+ * discarding, so long as it is done consistently for a group (for instance
* if the device is an mdev device where it is known that the host vendor
* driver will never pin pages outside of the working set of the guest
- * driver, which would thus not be ballooning candidates).
+ * driver, which would thus not be discarding candidates).
*
* The first opportunity to induce pinning occurs here where we attempt to
* attach the group to existing containers within the AddressSpace. If any
- * pages are already zapped from the virtual address space, such as from a
- * previous ballooning opt-in, new pinning will cause valid mappings to be
+ * pages are already zapped from the virtual address space, such as from
+ * previous discards, new pinning will cause valid mappings to be
* re-established. Likewise, when the overall MemoryListener for a new
* container is registered, a replay of mappings within the AddressSpace
* will occur, re-establishing any previously zapped pages as well.
*
- * NB. Balloon inhibiting does not currently block operation of the
- * balloon driver or revoke previously pinned pages, it only prevents
- * calling madvise to modify the virtual mapping of ballooned pages.
+ * Especially virtio-balloon is currently only prevented from discarding
+ * new memory, it will not yet set ram_block_discard_set_required() and
+ * therefore, neither stops us here or deals with the sudden memory
+ * consumption of inflated memory.
*/
- qemu_balloon_inhibit(true);
+ ret = ram_block_discard_disable(true);
+ if (ret) {
+ error_setg_errno(errp, -ret, "Cannot set discarding of RAM broken");
+ return ret;
+ }

QLIST_FOREACH(container, &space->containers, next) {
if (!ioctl(group->fd, VFIO_GROUP_SET_CONTAINER, &container->fd)) {
@@ -1405,7 +1409,7 @@ close_fd_exit:
close(fd);

put_space_exit:
- qemu_balloon_inhibit(false);
+ ram_block_discard_disable(false);
vfio_put_address_space(space);

return ret;
@@ -1526,8 +1530,8 @@ void vfio_put_group(VFIOGroup *group)
return;
}

- if (!group->balloon_allowed) {
- qemu_balloon_inhibit(false);
+ if (!group->ram_block_discard_allowed) {
+ ram_block_discard_disable(false);
}
vfio_kvm_device_del_group(group);
vfio_disconnect_container(group);
@@ -1565,22 +1569,23 @@ int vfio_get_device(VFIOGroup *group, const char *name,
}

/*
- * Clear the balloon inhibitor for this group if the driver knows the
- * device operates compatibly with ballooning. Setting must be consistent
- * per group, but since compatibility is really only possible with mdev
- * currently, we expect singleton groups.
+ * Set discarding of RAM as not broken for this group if the driver knows
+ * the device operates compatibly with discarding. Setting must be
+ * consistent per group, but since compatibility is really only possible
+ * with mdev currently, we expect singleton groups.
*/
- if (vbasedev->balloon_allowed != group->balloon_allowed) {
+ if (vbasedev->ram_block_discard_allowed !=
+ group->ram_block_discard_allowed) {
if (!QLIST_EMPTY(&group->device_list)) {
- error_setg(errp,
- "Inconsistent device balloon setting within group");
+ error_setg(errp, "Inconsistent setting of support for discarding "
+ "RAM (e.g., balloon) within group");
close(fd);
return -1;
}

- if (!group->balloon_allowed) {
- group->balloon_allowed = true;
- qemu_balloon_inhibit(false);
+ if (!group->ram_block_discard_allowed) {
+ group->ram_block_discard_allowed = true;
+ ram_block_discard_disable(false);
}
}

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 342dd6b912..c33c11b7e4 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2796,7 +2796,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
}

/*
- * Mediated devices *might* operate compatibly with memory ballooning, but
+ * Mediated devices *might* operate compatibly with discarding of RAM, but
* we cannot know for certain, it depends on whether the mdev vendor driver
* stays in sync with the active working set of the guest driver. Prevent
* the x-balloon-allowed option unless this is minimally an mdev device.
@@ -2809,7 +2809,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)

trace_vfio_mdev(vdev->vbasedev.name, is_mdev);

- if (vdev->vbasedev.balloon_allowed && !is_mdev) {
+ if (vdev->vbasedev.ram_block_discard_allowed && !is_mdev) {
error_setg(errp, "x-balloon-allowed only potentially compatible "
"with mdev devices");
vfio_put_group(group);
@@ -3163,7 +3163,7 @@ static Property vfio_pci_dev_properties[] = {
VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false),
DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false),
DEFINE_PROP_BOOL("x-balloon-allowed", VFIOPCIDevice,
- vbasedev.balloon_allowed, false),
+ vbasedev.ram_block_discard_allowed, false),
DEFINE_PROP_BOOL("x-no-kvm-intx", VFIOPCIDevice, no_kvm_intx, false),
DEFINE_PROP_BOOL("x-no-kvm-msi", VFIOPCIDevice, no_kvm_msi, false),
DEFINE_PROP_BOOL("x-no-kvm-msix", VFIOPCIDevice, no_kvm_msix, false),
diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index fd564209ac..c78f3ff559 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -108,7 +108,7 @@ typedef struct VFIODevice {
bool reset_works;
bool needs_reset;
bool no_mmap;
- bool balloon_allowed;
+ bool ram_block_discard_allowed;
VFIODeviceOps *ops;
unsigned int num_irqs;
unsigned int num_regions;
@@ -128,7 +128,7 @@ typedef struct VFIOGroup {
QLIST_HEAD(, VFIODevice) device_list;
QLIST_ENTRY(VFIOGroup) next;
QLIST_ENTRY(VFIOGroup) container_next;
- bool balloon_allowed;
+ bool ram_block_discard_allowed;
} VFIOGroup;

typedef struct VFIODMABuf {
--
2.25.4