[PATCH v4 2/3] xen/arm: reimplement xen_dma_unmap_page & friends
Stefano Stabellini
stefano.stabellini at eu.citrix.com
Fri Aug 8 10:03:10 PDT 2014
xen_dma_unmap_page, xen_dma_sync_single_for_cpu and
xen_dma_sync_single_for_device are currently implemented by calling into
the corresponding generic ARM implementation of these functions. In
order to do this, firstly the dma_addr_t handle, that on Xen is a
machine address, needs to be translated into a physical address. The
operation is expensive and inaccurate, given that a single machine
address can correspond to multiple physical addresses in one domain,
because the same page can be granted multiple times by the frontend.
To avoid this problem, we introduce a Xen specific implementation of
xen_dma_unmap_page, xen_dma_sync_single_for_cpu and
xen_dma_sync_single_for_device, that can operate on machine addresses
directly.
The new implementation relies on the fact that the hypervisor creates a
second p2m mapping of any grant pages at physical address == machine
address of the page for dom0. Therefore we can access memory at physical
address == dma_addr_r handle and perform the cache flushing there. Some
cache maintenance operations require a virtual address. Instead of using
ioremap_cache, that is not safe in interrupt context, we allocate a
per-cpu PAGE_KERNEL scratch page and we manually update the pte for it.
arm64 doesn't need cache maintenance operations on unmap for now.
Signed-off-by: Stefano Stabellini <stefano.stabellini at eu.citrix.com>
Tested-by: Denis Schneider <v1ne2go at gmail.com>
---
Changes in v4:
- fix wrong DMA_TO_DEVICE check in __xen_dma_page_dev_to_cpu.
Changes in v3:
- rename XENFEAT_grant_map_11 to XENFEAT_grant_map_identity.
Changes in v2:
- check for XENFEAT_grant_map_11;
- remeber the ptep corresponding to scratch pages so that we don't need
to calculate it again every time;
- do not acutally unmap the page on xen_mm32_unmap;
- properly account preempt_enable/disable.
---
arch/arm/include/asm/xen/page-coherent.h | 25 ++--
arch/arm/xen/Makefile | 2 +-
arch/arm/xen/mm32.c | 202 ++++++++++++++++++++++++++++++
3 files changed, 210 insertions(+), 19 deletions(-)
create mode 100644 arch/arm/xen/mm32.c
diff --git a/arch/arm/include/asm/xen/page-coherent.h b/arch/arm/include/asm/xen/page-coherent.h
index 1109017..e8275ea 100644
--- a/arch/arm/include/asm/xen/page-coherent.h
+++ b/arch/arm/include/asm/xen/page-coherent.h
@@ -26,25 +26,14 @@ static inline void xen_dma_map_page(struct device *hwdev, struct page *page,
__generic_dma_ops(hwdev)->map_page(hwdev, page, offset, size, dir, attrs);
}
-static inline void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
+void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
size_t size, enum dma_data_direction dir,
- struct dma_attrs *attrs)
-{
- if (__generic_dma_ops(hwdev)->unmap_page)
- __generic_dma_ops(hwdev)->unmap_page(hwdev, handle, size, dir, attrs);
-}
+ struct dma_attrs *attrs);
-static inline void xen_dma_sync_single_for_cpu(struct device *hwdev,
- dma_addr_t handle, size_t size, enum dma_data_direction dir)
-{
- if (__generic_dma_ops(hwdev)->sync_single_for_cpu)
- __generic_dma_ops(hwdev)->sync_single_for_cpu(hwdev, handle, size, dir);
-}
+void xen_dma_sync_single_for_cpu(struct device *hwdev,
+ dma_addr_t handle, size_t size, enum dma_data_direction dir);
+
+void xen_dma_sync_single_for_device(struct device *hwdev,
+ dma_addr_t handle, size_t size, enum dma_data_direction dir);
-static inline void xen_dma_sync_single_for_device(struct device *hwdev,
- dma_addr_t handle, size_t size, enum dma_data_direction dir)
-{
- if (__generic_dma_ops(hwdev)->sync_single_for_device)
- __generic_dma_ops(hwdev)->sync_single_for_device(hwdev, handle, size, dir);
-}
#endif /* _ASM_ARM_XEN_PAGE_COHERENT_H */
diff --git a/arch/arm/xen/Makefile b/arch/arm/xen/Makefile
index 1296952..1f85bfe 100644
--- a/arch/arm/xen/Makefile
+++ b/arch/arm/xen/Makefile
@@ -1 +1 @@
-obj-y := enlighten.o hypercall.o grant-table.o p2m.o mm.o
+obj-y := enlighten.o hypercall.o grant-table.o p2m.o mm.o mm32.o
diff --git a/arch/arm/xen/mm32.c b/arch/arm/xen/mm32.c
new file mode 100644
index 0000000..3b99860
--- /dev/null
+++ b/arch/arm/xen/mm32.c
@@ -0,0 +1,202 @@
+#include <linux/cpu.h>
+#include <linux/dma-mapping.h>
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+
+#include <xen/features.h>
+
+static DEFINE_PER_CPU(unsigned long, xen_mm32_scratch_virt);
+static DEFINE_PER_CPU(pte_t *, xen_mm32_scratch_ptep);
+
+static int alloc_xen_mm32_scratch_page(int cpu)
+{
+ struct page *page;
+ unsigned long virt;
+ pmd_t *pmdp;
+ pte_t *ptep;
+
+ if (per_cpu(xen_mm32_scratch_ptep, cpu) != NULL)
+ return 0;
+
+ page = alloc_page(GFP_KERNEL);
+ if (page == NULL) {
+ pr_warn("Failed to allocate xen_mm32_scratch_page for cpu %d\n", cpu);
+ return -ENOMEM;
+ }
+
+ virt = (unsigned long)__va(page_to_phys(page));
+ pmdp = pmd_offset(pud_offset(pgd_offset_k(virt), virt), virt);
+ ptep = pte_offset_kernel(pmdp, virt);
+
+ per_cpu(xen_mm32_scratch_virt, cpu) = virt;
+ per_cpu(xen_mm32_scratch_ptep, cpu) = ptep;
+
+ return 0;
+}
+
+static int xen_mm32_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ int cpu = (long)hcpu;
+ switch (action) {
+ case CPU_UP_PREPARE:
+ if (alloc_xen_mm32_scratch_page(cpu))
+ return NOTIFY_BAD;
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block xen_mm32_cpu_notifier = {
+ .notifier_call = xen_mm32_cpu_notify,
+};
+
+static void* xen_mm32_remap_page(dma_addr_t handle)
+{
+ unsigned long virt = get_cpu_var(xen_mm32_scratch_virt);
+ pte_t *ptep = __get_cpu_var(xen_mm32_scratch_ptep);
+
+ *ptep = pfn_pte(handle >> PAGE_SHIFT, PAGE_KERNEL);
+ local_flush_tlb_kernel_page(virt);
+
+ return (void*)virt;
+}
+
+static void xen_mm32_unmap(void *vaddr)
+{
+ put_cpu_var(xen_mm32_scratch_virt);
+}
+
+
+/* functions called by SWIOTLB */
+
+static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
+ size_t size, enum dma_data_direction dir,
+ void (*op)(const void *, size_t, int))
+{
+ unsigned long pfn;
+ size_t left = size;
+
+ pfn = (handle >> PAGE_SHIFT) + offset / PAGE_SIZE;
+ offset %= PAGE_SIZE;
+
+ do {
+ size_t len = left;
+ void *vaddr;
+
+ if (!pfn_valid(pfn))
+ {
+ /* Cannot map the page, we don't know its physical address.
+ * Return and hope for the best */
+ if (!xen_feature(XENFEAT_grant_map_identity))
+ return;
+ vaddr = xen_mm32_remap_page(handle) + offset;
+ op(vaddr, len, dir);
+ xen_mm32_unmap(vaddr - offset);
+ } else {
+ struct page *page = pfn_to_page(pfn);
+
+ if (PageHighMem(page)) {
+ if (len + offset > PAGE_SIZE)
+ len = PAGE_SIZE - offset;
+
+ if (cache_is_vipt_nonaliasing()) {
+ vaddr = kmap_atomic(page);
+ op(vaddr + offset, len, dir);
+ kunmap_atomic(vaddr);
+ } else {
+ vaddr = kmap_high_get(page);
+ if (vaddr) {
+ op(vaddr + offset, len, dir);
+ kunmap_high(page);
+ }
+ }
+ } else {
+ vaddr = page_address(page) + offset;
+ op(vaddr, len, dir);
+ }
+ }
+
+ offset = 0;
+ pfn++;
+ left -= len;
+ } while (left);
+}
+
+static void __xen_dma_page_dev_to_cpu(struct device *hwdev, dma_addr_t handle,
+ size_t size, enum dma_data_direction dir)
+{
+ /* Cannot use __dma_page_dev_to_cpu because we don't have a
+ * struct page for handle */
+
+ if (dir != DMA_TO_DEVICE)
+ outer_inv_range(handle, handle + size);
+
+ dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, dmac_unmap_area);
+}
+
+static void __xen_dma_page_cpu_to_dev(struct device *hwdev, dma_addr_t handle,
+ size_t size, enum dma_data_direction dir)
+{
+
+ dma_cache_maint(handle & PAGE_MASK, handle & ~PAGE_MASK, size, dir, dmac_map_area);
+
+ if (dir == DMA_FROM_DEVICE) {
+ outer_inv_range(handle, handle + size);
+ } else {
+ outer_clean_range(handle, handle + size);
+ }
+}
+
+void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle,
+ size_t size, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+{
+ if (!__generic_dma_ops(hwdev)->unmap_page)
+ return;
+ if (dma_get_attr(DMA_ATTR_SKIP_CPU_SYNC, attrs))
+ return;
+
+ __xen_dma_page_dev_to_cpu(hwdev, handle, size, dir);
+}
+
+void xen_dma_sync_single_for_cpu(struct device *hwdev,
+ dma_addr_t handle, size_t size, enum dma_data_direction dir)
+{
+ if (!__generic_dma_ops(hwdev)->sync_single_for_cpu)
+ return;
+ __xen_dma_page_dev_to_cpu(hwdev, handle, size, dir);
+}
+
+void xen_dma_sync_single_for_device(struct device *hwdev,
+ dma_addr_t handle, size_t size, enum dma_data_direction dir)
+{
+ if (!__generic_dma_ops(hwdev)->sync_single_for_device)
+ return;
+ __xen_dma_page_cpu_to_dev(hwdev, handle, size, dir);
+}
+
+int __init xen_mm32_init(void)
+{
+ int cpu;
+
+ if (!xen_initial_domain())
+ return 0;
+
+ register_cpu_notifier(&xen_mm32_cpu_notifier);
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ if (alloc_xen_mm32_scratch_page(cpu)) {
+ put_online_cpus();
+ unregister_cpu_notifier(&xen_mm32_cpu_notifier);
+ return -ENOMEM;
+ }
+ }
+ put_online_cpus();
+
+ return 0;
+}
+arch_initcall(xen_mm32_init);
--
1.7.10.4
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