WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] Re: [PATCH] xen: modify kernel mappings corresponding to gra

On Tue, Jul 26, 2011 at 05:55:45PM +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.
> On x86_64 it is easy, we can issue another HYPERVISOR_grant_table_op
> right away in m2p_add_override. We can remove the mappings using another
> HYPERVISOR_grant_table_op in m2p_remove_override.
> On x86_32 it is more difficult because the pages are highmem pages and
> therefore we need to catch the set_pte that tries to map a granted page
> and issue an HYPERVISOR_grant_table_op instead.
> Same thing for unmapping them: we need to catch the pte clear or the
> set_pte that try to unmap a granted page and issue an
> HYPERVISOR_grant_table_op.

So I hadn't looked at this in detail, but I wonder if we can use the
MULTIcall for this? It looks like we need to do two hypercalls so why
not batch it?

And while we are it - we could change the MMU ops to only do this on
initial domain and for the domU case do the old mechanism? In essence
adding two variants of the xen_set_pte - domU and dom0? .. And we
should get rid of the debug one (xen_set_pte_debug) - it has helped a bit
but I don't think anybody is using it except me.

> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/xen/page.h |    5 ++-
>  arch/x86/xen/mmu.c              |   68 
> +++++++++++++++++++++++++++++++++++++++
>  arch/x86/xen/p2m.c              |   47 ++++++++++++++++++++------
>  drivers/xen/gntdev.c            |   27 +++++++++++++++-
>  drivers/xen/grant-table.c       |    4 +-
>  include/xen/grant_table.h       |    1 +
>  6 files changed, 137 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 64a619d..ec7bbfb 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/mmu.c b/arch/x86/xen/mmu.c
> index 4e37a7c0..13f20d8 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -282,8 +282,70 @@ static bool xen_batched_set_pte(pte_t *ptep, pte_t 
> pteval)
>       return true;
>  }
>  
> +#ifdef CONFIG_HIGHMEM
> +static int xen_unmap_granted_page(pte_t *ptep)
> +{
> +     unsigned long mfn;
> +     struct page *page;
> +
> +     if (pte_flags(*ptep) & _PAGE_USER)
> +             return 1;
> +     mfn = (ptep->pte & PTE_PFN_MASK) >> PAGE_SHIFT;
> +     page = m2p_find_override(mfn);
> +     if (page != NULL && (page->private & GRANT_FRAME_BIT)) {
> +             int ret;
> +             struct gnttab_unmap_grant_ref kunmap_op;
> +             struct gnttab_map_grant_ref *kmap_op =
> +                     (struct gnttab_map_grant_ref *) page->index;
> +             kunmap_op.host_addr = kmap_op->host_addr;
> +             kunmap_op.handle = kmap_op->handle;
> +             kunmap_op.dev_bus_addr = 0;
> +             ret = HYPERVISOR_grant_table_op(
> +                             GNTTABOP_unmap_grant_ref, &kunmap_op, 1);
> +             WARN(ret, "m2p_remove_override: pfn %lx mfn %lx, failed to "
> +                     "modify kernel mappings", page_to_pfn(page), mfn);
> +             return ret;
> +     }
> +     return 1;
> +}
> +#endif
> +
>  static void xen_set_pte(pte_t *ptep, pte_t pteval)
>  {
> +#ifdef CONFIG_HIGHMEM
> +     if (!(pte_flags(pteval) & _PAGE_USER)) {
> +             int ret;
> +             struct page *page;
> +             unsigned long mfn = (pteval.pte & PTE_PFN_MASK) >> PAGE_SHIFT;
> +             page = m2p_find_override(mfn);
> +             /*
> +              * if this is a granted page we need to use a grant table
> +              * hypercall to map it instead
> +              */
> +             if (page != NULL && (page->private & GRANT_FRAME_BIT)) {
> +                     struct gnttab_map_grant_ref *kmap_op =
> +                             (struct gnttab_map_grant_ref *) page->index;
> +                     unsigned long old_mfn = kmap_op->dev_bus_addr;
> +                     kmap_op->host_addr =
> +                             arbitrary_virt_to_machine(ptep).maddr;
> +                     kmap_op->dev_bus_addr = 0;
> +                     ret = HYPERVISOR_grant_table_op(
> +                                     GNTTABOP_map_grant_ref, kmap_op, 1);
> +                     WARN(ret, "xen_set_pte: pfn %lx mfn %lx, failed to "
> +                             "modify kernel mappings",
> +                             page_to_pfn(page), mfn);
> +                     kmap_op->dev_bus_addr = old_mfn;
> +                     return;
> +             }
> +             /*
> +              * even if it is not a granted page, the old page we are about
> +              * to overwrite could be a granted page and in that case we need
> +              * to unmap it using a grant table hypercall
> +              */
> +             xen_unmap_granted_page(ptep);
> +     }
> +#endif
> +
>       if (!xen_batched_set_pte(ptep, pteval))
>               native_set_pte(ptep, pteval);
>  }
> @@ -548,6 +610,12 @@ static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
>  
>  static void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t 
> *ptep)
>  {
> +     /*
> +      * check if this is a granted page and unmap it using a grant table
> +      * hypercall in that case
> +      */
> +     if (!xen_unmap_granted_page(ptep))
> +             return;
>       if (!xen_batched_set_pte(ptep, native_make_pte(0)))
>               native_pte_clear(mm, addr, ptep);
>  }
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 58efeb9..1c4d2b5 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -161,6 +161,7 @@
>  #include <asm/xen/page.h>
>  #include <asm/xen/hypercall.h>
>  #include <asm/xen/hypervisor.h>
> +#include <xen/grant_table.h>
>  
>  #include "xen-ops.h"
>  
> @@ -676,7 +677,8 @@ 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)
>  {
>       unsigned long flags;
>       unsigned long pfn;
> @@ -699,9 +701,18 @@ 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)) {
> +                     int ret = HYPERVISOR_grant_table_op(
> +                                     GNTTABOP_map_grant_ref, kmap_op, 1);
> +                     WARN(ret, "m2p_add_override: pfn %lx mfn %lx, "
> +                             "failed to modify kernel mappings", pfn, mfn);
> +             }
> +             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 +746,27 @@ 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)) {
> +                     int ret;
> +                     struct gnttab_unmap_grant_ref unmap_op;
> +                     unmap_op.host_addr = map_op->host_addr;
> +                     unmap_op.handle = map_op->handle;
> +                     unmap_op.dev_bus_addr = 0;
> +                     ret = HYPERVISOR_grant_table_op(
> +                                     GNTTABOP_unmap_grant_ref, &unmap_op, 1);
> +                     WARN(ret, "m2p_remove_override: pfn %lx mfn %lx, "
> +                             "failed to modify kernel mappings", pfn, mfn);
> +                     set_pte_at(&init_mm, address, ptep,
> +                                     pfn_pte(pfn, PAGE_KERNEL));
> +                     __flush_tlb_single(address);
> +             }
> +     } else
> +             set_phys_to_machine(pfn, page->index);
>  
>       return 0;
>  }
> @@ -758,7 +783,7 @@ 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 f914b26..ca41772 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 fd725cd..1e8669a 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

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel