lkml.org 
[lkml]   [2011]   [Sep]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [Xen-devel] Re: [PATCH 0/6] xen: don't call vmalloc_sync_all() when mapping foreign pages
On 15/09/11 22:37, Jeremy Fitzhardinge wrote:
> On 09/15/2011 05:40 AM, David Vrabel wrote:
>> This set of pages avoids the need to call vmalloc_sync_all() when
>> mapping foreign pages. Two new functions are adding for mapping
>> foreign pages onto RAM pages instead of vmalloc space.
>>
>> [...]
>
> But that said, if you want to allocate virtual addresses for mapping
> granted pages, then alloc_vm_area() is the right thing to use. You need
> to make sure you touch the pages from within the kernel before passing
> those addresses to a hypercall to make sure the mappings are established
> within the current task (possibly within a no-preempt region to
> guarantee that nothing odd happens). Or alternatively, you could switch
> the current pagetable to init_mm for the hypercall (if it isn't already)
> - since that's the reference pagetable - assuming you're not passing
> usermode virtual addresses to the hypercall.

Making alloc_vm_area() fill in a array of pte_t *'s and passing the pointer
to the PTE (using the GNTMAP_contains_pte flag) in the hypercall should
allow Xen to update the PTEs in init_mm directly.

However, I'm not sure what to do about ia64 where GNTMAP_contains_pte
is not supported. Any ideas?

Here's the untested patch I have so far.

diff --git a/arch/x86/xen/grant-table.c b/arch/x86/xen/grant-table.c
index 49ba9b5..77348e8 100644
--- a/arch/x86/xen/grant-table.c
+++ b/arch/x86/xen/grant-table.c
@@ -71,7 +71,7 @@ int arch_gnttab_map_shared(unsigned long *frames, unsigned long nr_gframes,

if (shared == NULL) {
struct vm_struct *area =
- alloc_vm_area(PAGE_SIZE * max_nr_gframes);
+ alloc_vm_area(PAGE_SIZE * max_nr_gframes, NULL);
BUG_ON(area == NULL);
shared = area->addr;
*__shared = shared;
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index cdacf92..75eb179 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -435,19 +435,20 @@ EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
int xenbus_map_ring_valloc(struct xenbus_device *dev, int gnt_ref, void **vaddr)
{
struct gnttab_map_grant_ref op = {
- .flags = GNTMAP_host_map,
+ .flags = GNTMAP_host_map | GNTMAP_contains_pte,
.ref = gnt_ref,
.dom = dev->otherend_id,
};
struct vm_struct *area;
+ pte_t *pte;

*vaddr = NULL;

- area = alloc_vm_area(PAGE_SIZE);
+ area = alloc_vm_area(PAGE_SIZE, &pte);
if (!area)
return -ENOMEM;

- op.host_addr = (unsigned long)area->addr;
+ op.host_addr = (unsigned long)pte;

if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
BUG();
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 9332e52..1a77252 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -118,7 +118,7 @@ unmap_kernel_range(unsigned long addr, unsigned long size)
#endif

/* Allocate/destroy a 'vmalloc' VM area. */
-extern struct vm_struct *alloc_vm_area(size_t size);
+extern struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes);
extern void free_vm_area(struct vm_struct *area);

/* for /dev/kmem */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5016f19..786b4f6 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2105,23 +2105,30 @@ void __attribute__((weak)) vmalloc_sync_all(void)

static int f(pte_t *pte, pgtable_t table, unsigned long addr, void *data)
{
- /* apply_to_page_range() does all the hard work. */
+ pte_t ***p = data;
+
+ if (p) {
+ *(*p) = pte;
+ (*p)++;
+ }
return 0;
}

/**
* alloc_vm_area - allocate a range of kernel address space
* @size: size of the area
+ * @ptes: returns the PTEs for the address space
*
* Returns: NULL on failure, vm_struct on success
*
* This function reserves a range of kernel address space, and
* allocates pagetables to map that range. No actual mappings
- * are created. If the kernel address space is not shared
- * between processes, it syncs the pagetable across all
- * processes.
+ * are created.
+ *
+ * If @ptes is non-NULL, pointers to the PTEs (in init_mm)
+ * allocated for the VM area are returned.
*/
-struct vm_struct *alloc_vm_area(size_t size)
+struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes)
{
struct vm_struct *area;

@@ -2135,19 +2142,11 @@ struct vm_struct *alloc_vm_area(size_t size)
* of kernel virtual address space and mapped into init_mm.
*/
if (apply_to_page_range(&init_mm, (unsigned long)area->addr,
- area->size, f, NULL)) {
+ area->size, f, ptes ? &ptes : NULL)) {
free_vm_area(area);
return NULL;
}

- /*
- * If the allocated address space is passed to a hypercall
- * before being used then we cannot rely on a page fault to
- * trigger an update of the page tables. So sync all the page
- * tables here.
- */
- vmalloc_sync_all();
-
return area;
}
EXPORT_SYMBOL_GPL(alloc_vm_area);
David


\
 
 \ /
  Last update: 2011-09-21 16:47    [W:0.073 / U:1.644 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site