Re: [PATCH v3 2/2] xen: modify kernel mappings corresponding togranted pages

From: Konrad Rzeszutek Wilk
Date: Wed Sep 07 2011 - 18:28:27 EST

On Wed, Sep 07, 2011 at 05:39:31PM +0100, stefano.stabellini@xxxxxxxxxxxxx wrote:
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
>
> If we want to use granted pages for AIO, changing the mappings of a user
> vma and the corresponding p2m is not enough, we also need to update the
> kernel mappings accordingly.
> In order to avoid the complexity of dealing with highmem, we allocated
> the pages lowmem.
> We issue a HYPERVISOR_grant_table_op right away in
> m2p_add_override and we remove the mappings using another
> HYPERVISOR_grant_table_op in m2p_remove_override.
> Considering that m2p_add_override and m2p_remove_override are called
> once per page we use multicalls and hypercall batching.
>
> Use the kmap_op pointer directly as argument to do the mapping as it is
> guaranteed to be present up until the unmapping is done.
> Before issuing any unmapping multicalls, we need to make sure that the
> mapping has already being done, because we need the kmap->handle to be
> set correctly.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/xen/page.h | 5 ++-
> arch/x86/xen/p2m.c | 67 ++++++++++++++++++++++++++++++++------
> drivers/xen/gntdev.c | 27 +++++++++++++++-
> drivers/xen/grant-table.c | 4 +-
> include/xen/grant_table.h | 1 +
> 5 files changed, 89 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 7ff4669..0ce1884 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -12,6 +12,7 @@
> #include <asm/pgtable.h>
>
> #include <xen/interface/xen.h>
> +#include <xen/grant_table.h>
> #include <xen/features.h>
>
> /* Xen machine address */
> @@ -31,8 +32,10 @@ typedef struct xpaddr {
> #define INVALID_P2M_ENTRY (~0UL)
> #define FOREIGN_FRAME_BIT (1UL<<(BITS_PER_LONG-1))
> #define IDENTITY_FRAME_BIT (1UL<<(BITS_PER_LONG-2))
> +#define GRANT_FRAME_BIT (1UL<<(BITS_PER_LONG-3))
> #define FOREIGN_FRAME(m) ((m) | FOREIGN_FRAME_BIT)
> #define IDENTITY_FRAME(m) ((m) | IDENTITY_FRAME_BIT)
> +#define GRANT_FRAME(m) ((m) | GRANT_FRAME_BIT)
>
> /* Maximum amount of memory we can handle in a domain in pages */
> #define MAX_DOMAIN_PAGES \
> @@ -48,7 +51,7 @@ extern unsigned long set_phys_range_identity(unsigned long pfn_s,
> unsigned long pfn_e);
>
> extern int m2p_add_override(unsigned long mfn, struct page *page,
> - bool clear_pte);
> + struct gnttab_map_grant_ref *kmap_op);
> extern int m2p_remove_override(struct page *page, bool clear_pte);
> extern struct page *m2p_find_override(unsigned long mfn);
> extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 58efeb9..6c26ac80 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -161,7 +161,9 @@
> #include <asm/xen/page.h>
> #include <asm/xen/hypercall.h>
> #include <asm/xen/hypervisor.h>
> +#include <xen/grant_table.h>
>
> +#include "multicalls.h"
> #include "xen-ops.h"
>
> static void __init m2p_override_init(void);
> @@ -676,7 +678,8 @@ static unsigned long mfn_hash(unsigned long mfn)
> }
>
> /* Add an MFN override for a particular page */
> -int m2p_add_override(unsigned long mfn, struct page *page, bool clear_pte)
> +int m2p_add_override(unsigned long mfn, struct page *page,
> + struct gnttab_map_grant_ref *kmap_op)

So how come you ripped out 'clear_pte' here but left it in
m2p_remove_override? Is it b/c you aren't doing the pte_clear in
the first place?

Also there are other users of 'm2p_add_override' that you hadn't modified
(blkback.c) so it will cause an compile failure.

Please also test this patchset with the blkback in the picture to make
sure this: cf8d91633ddef9e816ccbf3da833c79ce508988d
does not happen.

> {
> unsigned long flags;
> unsigned long pfn;
> @@ -699,9 +702,20 @@ int m2p_add_override(unsigned long mfn, struct page *page, bool clear_pte)
> if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
> return -ENOMEM;
>
> - if (clear_pte && !PageHighMem(page))
> - /* Just zap old mapping for now */
> - pte_clear(&init_mm, address, ptep);
> + if (kmap_op != NULL) {
> + if (!PageHighMem(page)) {
> + struct multicall_space mcs = xen_mc_entry(sizeof(*kmap_op));
> +
> + MULTI_grant_table_op(mcs.mc,
> + GNTTABOP_map_grant_ref, kmap_op, 1);
> +
> + xen_mc_issue(PARAVIRT_LAZY_MMU);
> + }
> + page->private |= GRANT_FRAME_BIT;
> + /* let's use dev_bus_addr to record the old mfn instead */
> + kmap_op->dev_bus_addr = page->index;
> + page->index = (unsigned long) kmap_op;
> + }
> spin_lock_irqsave(&m2p_override_lock, flags);
> list_add(&page->lru, &m2p_overrides[mfn_hash(mfn)]);
> spin_unlock_irqrestore(&m2p_override_lock, flags);
> @@ -735,13 +749,44 @@ int m2p_remove_override(struct page *page, bool clear_pte)
> spin_lock_irqsave(&m2p_override_lock, flags);
> list_del(&page->lru);
> spin_unlock_irqrestore(&m2p_override_lock, flags);
> - set_phys_to_machine(pfn, page->index);
>
> - if (clear_pte && !PageHighMem(page))
> - set_pte_at(&init_mm, address, ptep,
> - pfn_pte(pfn, PAGE_KERNEL));
> - /* No tlb flush necessary because the caller already
> - * left the pte unmapped. */
> + if (clear_pte) {
> + struct gnttab_map_grant_ref *map_op =
> + (struct gnttab_map_grant_ref *) page->index;
> + set_phys_to_machine(pfn, map_op->dev_bus_addr);
> + if (!PageHighMem(page)) {
> + struct multicall_space mcs =
> + xen_mc_entry(sizeof(struct gnttab_unmap_grant_ref));
> + struct gnttab_unmap_grant_ref *unmap_op = mcs.args;
> +
> + /*

scripts/checkpath.pl will throw a fit at the above.

> + * Has the grant_op mapping multicall being issued? If not,
> + * make sure it is called now.
> + */
> + if (map_op->handle == -1)
> + xen_mc_flush();
> + if (map_op->handle == -1) {
> + printk(KERN_WARNING "m2p_remove_override: pfn %lx mfn %lx, "
> + "failed to modify kernel mappings", pfn, mfn);
> + return -1;
> + }
> +
> + unmap_op->host_addr = map_op->host_addr;
> + unmap_op->handle = map_op->handle;
> + unmap_op->dev_bus_addr = 0;
> +
> + MULTI_grant_table_op(mcs.mc,
> + GNTTABOP_unmap_grant_ref, unmap_op, 1);
> +
> + xen_mc_issue(PARAVIRT_LAZY_MMU);
> +
> + set_pte_at(&init_mm, address, ptep,
> + pfn_pte(pfn, PAGE_KERNEL));
> + __flush_tlb_single(address);
> + map_op->host_addr = 0;
> + }
> + } else
> + set_phys_to_machine(pfn, page->index);
>
> return 0;
> }
> @@ -758,7 +803,7 @@ struct page *m2p_find_override(unsigned long mfn)
> spin_lock_irqsave(&m2p_override_lock, flags);
>
> list_for_each_entry(p, bucket, lru) {
> - if (p->private == mfn) {
> + if ((p->private & (~GRANT_FRAME_BIT)) == mfn) {
> ret = p;
> break;
> }
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 07a56c2..783aaad 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -83,6 +83,7 @@ struct grant_map {
> struct ioctl_gntdev_grant_ref *grants;
> struct gnttab_map_grant_ref *map_ops;
> struct gnttab_unmap_grant_ref *unmap_ops;
> + struct gnttab_map_grant_ref *kmap_ops;
> struct page **pages;
> };
>
> @@ -116,10 +117,12 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> add->grants = kzalloc(sizeof(add->grants[0]) * count, GFP_KERNEL);
> add->map_ops = kzalloc(sizeof(add->map_ops[0]) * count, GFP_KERNEL);
> add->unmap_ops = kzalloc(sizeof(add->unmap_ops[0]) * count, GFP_KERNEL);
> + add->kmap_ops = kzalloc(sizeof(add->kmap_ops[0]) * count, GFP_KERNEL);
> add->pages = kzalloc(sizeof(add->pages[0]) * count, GFP_KERNEL);
> if (NULL == add->grants ||
> NULL == add->map_ops ||
> NULL == add->unmap_ops ||
> + NULL == add->kmap_ops ||
> NULL == add->pages)
> goto err;
>
> @@ -129,6 +132,7 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> for (i = 0; i < count; i++) {
> add->map_ops[i].handle = -1;
> add->unmap_ops[i].handle = -1;
> + add->kmap_ops[i].handle = -1;
> }
>
> add->index = 0;
> @@ -142,6 +146,7 @@ err:
> kfree(add->grants);
> kfree(add->map_ops);
> kfree(add->unmap_ops);
> + kfree(add->kmap_ops);
> kfree(add);
> return NULL;
> }
> @@ -243,10 +248,30 @@ static int map_grant_pages(struct grant_map *map)
> gnttab_set_unmap_op(&map->unmap_ops[i], addr,
> map->flags, -1 /* handle */);
> }
> + } else {
> + for (i = 0; i < map->count; i++) {
> + unsigned level;
> + unsigned long address = (unsigned long)
> + pfn_to_kaddr(page_to_pfn(map->pages[i]));
> + pte_t *ptep;
> + u64 pte_maddr = 0;
> + if (!PageHighMem(map->pages[i])) {
> + ptep = lookup_address(address, &level);
> + pte_maddr =
> + arbitrary_virt_to_machine(ptep).maddr;
> + }
> + gnttab_set_map_op(&map->kmap_ops[i], pte_maddr,
> + map->flags |
> + GNTMAP_host_map |
> + GNTMAP_contains_pte,
> + map->grants[i].ref,
> + map->grants[i].domid);
> + }
> }
>
> pr_debug("map %d+%d\n", map->index, map->count);
> - err = gnttab_map_refs(map->map_ops, map->pages, map->count);
> + err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
> + map->pages, map->count);
> if (err)
> return err;
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 4f44b34..ed6622f 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -448,6 +448,7 @@ unsigned int gnttab_max_grant_frames(void)
> EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);
>
> int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> struct page **pages, unsigned int count)
> {
> int i, ret;
> @@ -488,8 +489,7 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> */
> return -EOPNOTSUPP;
> }
> - ret = m2p_add_override(mfn, pages[i],
> - map_ops[i].flags & GNTMAP_contains_pte);
> + ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
> if (ret)
> return ret;
> }
> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
> index b1fab6b..6b99bfb 100644
> --- a/include/xen/grant_table.h
> +++ b/include/xen/grant_table.h
> @@ -156,6 +156,7 @@ unsigned int gnttab_max_grant_frames(void);
> #define gnttab_map_vaddr(map) ((void *)(map.host_virt_addr))
>
> int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> struct page **pages, unsigned int count);
> int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
> struct page **pages, unsigned int count);
> --
> 1.7.2.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/