Re: [PATCH V4 1/2] xen/virtio: Optimize the setup of "xen-grant-dma" devices

From: Xenia Ragiadakou
Date: Tue Oct 25 2022 - 13:27:25 EST

On 10/25/22 19:20, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

This is needed to avoid having to parse the same device-tree
several times for a given device.

For this to work we need to install the xen_virtio_restricted_mem_acc
callback in Arm's xen_guest_init() which is same callback as x86's
PV and HVM modes already use and remove the manual assignment in
xen_setup_dma_ops(). Also we need to split the code to initialize
backend_domid into a separate function.

Prior to current patch we parsed the device-tree three times:
1. xen_setup_dma_ops()->...->xen_is_dt_grant_dma_device()
2. xen_setup_dma_ops()->...->xen_dt_grant_init_backend_domid()
3. xen_virtio_mem_acc()->...->xen_is_dt_grant_dma_device()

With current patch we parse the device-tree only once in
xen_virtio_restricted_mem_acc()->...->xen_dt_grant_init_backend_domid()

Other benefits are:
- Not diverge from x86 when setting up Xen grant DMA ops
- Drop several global functions

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Reviewed-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>

I have a question unrelated to the patch.
CONFIG_XEN_VIRTIO_FORCE_GRANT cannot be used to force backend dom0 in case xen_dt_grant_init_backend_domid() fails?

---
New patch
---
arch/arm/xen/enlighten.c | 2 +-
drivers/xen/grant-dma-ops.c | 77 ++++++++++++++-----------------------
include/xen/arm/xen-ops.h | 4 +-
include/xen/xen-ops.h | 16 --------
4 files changed, 30 insertions(+), 69 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 93c8ccbf2982..7d59765aef22 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -445,7 +445,7 @@ static int __init xen_guest_init(void)
return 0;
if (IS_ENABLED(CONFIG_XEN_VIRTIO))
- virtio_set_mem_acc_cb(xen_virtio_mem_acc);
+ virtio_set_mem_acc_cb(xen_virtio_restricted_mem_acc);
if (!acpi_disabled)
xen_acpi_guest_init();
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index daa525df7bdc..1e797a043980 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -292,50 +292,20 @@ static const struct dma_map_ops xen_grant_dma_ops = {
.dma_supported = xen_grant_dma_supported,
};
-static bool xen_is_dt_grant_dma_device(struct device *dev)
-{
- struct device_node *iommu_np;
- bool has_iommu;
-
- iommu_np = of_parse_phandle(dev->of_node, "iommus", 0);
- has_iommu = iommu_np &&
- of_device_is_compatible(iommu_np, "xen,grant-dma");
- of_node_put(iommu_np);
-
- return has_iommu;
-}
-
-bool xen_is_grant_dma_device(struct device *dev)
-{
- /* XXX Handle only DT devices for now */
- if (dev->of_node)
- return xen_is_dt_grant_dma_device(dev);
-
- return false;
-}
-
-bool xen_virtio_mem_acc(struct virtio_device *dev)
-{
- if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain())
- return true;
-
- return xen_is_grant_dma_device(dev->dev.parent);
-}
-
static int xen_dt_grant_init_backend_domid(struct device *dev,
- struct xen_grant_dma_data *data)
+ domid_t *backend_domid)
{
struct of_phandle_args iommu_spec;
if (of_parse_phandle_with_args(dev->of_node, "iommus", "#iommu-cells",
0, &iommu_spec)) {
- dev_err(dev, "Cannot parse iommus property\n");
+ dev_dbg(dev, "Cannot parse iommus property\n");
return -ESRCH;
}
if (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
iommu_spec.args_count != 1) {
- dev_err(dev, "Incompatible IOMMU node\n");
+ dev_dbg(dev, "Incompatible IOMMU node\n");
of_node_put(iommu_spec.np);
return -ESRCH;
}
@@ -346,12 +316,28 @@ static int xen_dt_grant_init_backend_domid(struct device *dev,
* The endpoint ID here means the ID of the domain where the
* corresponding backend is running
*/
- data->backend_domid = iommu_spec.args[0];
+ *backend_domid = iommu_spec.args[0];
return 0;
}
-void xen_grant_setup_dma_ops(struct device *dev)
+static int xen_grant_init_backend_domid(struct device *dev,
+ domid_t *backend_domid)
+{
+ int ret = -ENODEV;
+
+ if (dev->of_node) {
+ ret = xen_dt_grant_init_backend_domid(dev, backend_domid);
+ } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain()) {
+ dev_info(dev, "Using dom0 as backend\n");
+ *backend_domid = 0;
+ ret = 0;
+ }
+
+ return ret;
+}
+
+static void xen_grant_setup_dma_ops(struct device *dev, domid_t backend_domid)
{
struct xen_grant_dma_data *data;
@@ -365,16 +351,7 @@ void xen_grant_setup_dma_ops(struct device *dev)
if (!data)
goto err;
- if (dev->of_node) {
- if (xen_dt_grant_init_backend_domid(dev, data))
- goto err;
- } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT)) {
- dev_info(dev, "Using dom0 as backend\n");
- data->backend_domid = 0;
- } else {
- /* XXX ACPI device unsupported for now */
- goto err;
- }
+ data->backend_domid = backend_domid;
if (store_xen_grant_dma_data(dev, data)) {
dev_err(dev, "Cannot store Xen grant DMA data\n");
@@ -392,12 +369,14 @@ void xen_grant_setup_dma_ops(struct device *dev)
bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
{
- bool ret = xen_virtio_mem_acc(dev);
+ domid_t backend_domid;
- if (ret)
- xen_grant_setup_dma_ops(dev->dev.parent);
+ if (!xen_grant_init_backend_domid(dev->dev.parent, &backend_domid)) {
+ xen_grant_setup_dma_ops(dev->dev.parent, backend_domid);
+ return true;
+ }
- return ret;
+ return false;
}
MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
diff --git a/include/xen/arm/xen-ops.h b/include/xen/arm/xen-ops.h
index b0766a660338..70073f5a2b54 100644
--- a/include/xen/arm/xen-ops.h
+++ b/include/xen/arm/xen-ops.h
@@ -8,9 +8,7 @@
static inline void xen_setup_dma_ops(struct device *dev)
{
#ifdef CONFIG_XEN
- if (xen_is_grant_dma_device(dev))
- xen_grant_setup_dma_ops(dev);
- else if (xen_swiotlb_detect())
+ if (xen_swiotlb_detect())
dev->dma_ops = &xen_swiotlb_dma_ops;
#endif
}
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index a34f4271a2e9..47f11bec5e90 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -216,26 +216,10 @@ static inline void xen_preemptible_hcall_end(void) { }
#endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */
#ifdef CONFIG_XEN_GRANT_DMA_OPS
-void xen_grant_setup_dma_ops(struct device *dev);
-bool xen_is_grant_dma_device(struct device *dev);
-bool xen_virtio_mem_acc(struct virtio_device *dev);
bool xen_virtio_restricted_mem_acc(struct virtio_device *dev);
#else
-static inline void xen_grant_setup_dma_ops(struct device *dev)
-{
-}
-static inline bool xen_is_grant_dma_device(struct device *dev)
-{
- return false;
-}
-
struct virtio_device;
-static inline bool xen_virtio_mem_acc(struct virtio_device *dev)
-{
- return false;
-}
-
static inline bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
{
return false;

--
Xenia