Re: [Xen-devel] [PATCH v5] xen/grant-table: Avoid m2p_overrideduring mapping

From: Konrad Rzeszutek Wilk
Date: Fri Jan 24 2014 - 09:38:27 EST

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On Thu, Jan 23, 2014 at 01:07:10PM +0000, Zoltan Kiss wrote:
> The grant mapping API does m2p_override unnecessarily: only gntdev needs it,
> for blkback and future netback patches it just cause a lock contention, as
> those pages never go to userspace. Therefore this series does the following:
> - the original functions were renamed to __gnttab_[un]map_refs, with a new
> parameter m2p_override
> - based on m2p_override either they follow the original behaviour, or just set
> the private flag and call set_phys_to_machine
> - gnttab_[un]map_refs are now a wrapper to call __gnttab_[un]map_refs with
> m2p_override false
> - a new function gnttab_[un]map_refs_userspace provides the old behaviour
>
> It also removes a stray space from page.h and change ret to 0 if
> XENFEAT_auto_translated_physmap, as that is the only possible return value
> there.
>
> v2:
> - move the storing of the old mfn in page->index to gnttab_map_refs
> - move the function header update to a separate patch
>
> v3:
> - a new approach to retain old behaviour where it needed
> - squash the patches into one
>
> v4:
> - move out the common bits from m2p* functions, and pass pfn/mfn as parameter
> - clear page->private before doing anything with the page, so m2p_find_override
> won't race with this
>
> v5:
> - change return value handling in __gnttab_[un]map_refs
> - remove a stray space in page.h
> - add detail why ret = 0 now at some places
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> Suggested-by: David Vrabel <david.vrabel@xxxxxxxxxx>

It looks OK to me and while it is not a bug-fix I think it should
go for v3.14 - as it _should_ improve the backends.

David or Boris; Stefano, please Ack/Nack it.

Thank you.
> ---
> arch/x86/include/asm/xen/page.h | 12 +++--
> arch/x86/xen/p2m.c | 25 ++--------
> drivers/block/xen-blkback/blkback.c | 15 +++---
> drivers/xen/gntdev.c | 13 +++--
> drivers/xen/grant-table.c | 90 ++++++++++++++++++++++++++++++-----
> include/xen/grant_table.h | 8 +++-
> 6 files changed, 109 insertions(+), 54 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index b913915..68a1438 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -49,10 +49,14 @@ extern bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn);
> 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,
> - struct gnttab_map_grant_ref *kmap_op);
> +extern int m2p_add_override(unsigned long mfn,
> + struct page *page,
> + struct gnttab_map_grant_ref *kmap_op,
> + unsigned long pfn);
> extern int m2p_remove_override(struct page *page,
> - struct gnttab_map_grant_ref *kmap_op);
> + struct gnttab_map_grant_ref *kmap_op,
> + unsigned long pfn,
> + unsigned long mfn);
> extern struct page *m2p_find_override(unsigned long mfn);
> extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
>
> @@ -121,7 +125,7 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
> pfn = m2p_find_override_pfn(mfn, ~0);
> }
>
> - /*
> + /*
> * pfn is ~0 if there are no entries in the m2p for mfn or if the
> * entry doesn't map back to the mfn and m2p_override doesn't have a
> * valid entry for it.
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 2ae8699..0060178 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -872,15 +872,13 @@ 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,
> - struct gnttab_map_grant_ref *kmap_op)
> + struct gnttab_map_grant_ref *kmap_op, unsigned long pfn)
> {
> unsigned long flags;
> - unsigned long pfn;
> unsigned long uninitialized_var(address);
> unsigned level;
> pte_t *ptep = NULL;
>
> - pfn = page_to_pfn(page);
> if (!PageHighMem(page)) {
> address = (unsigned long)__va(pfn << PAGE_SHIFT);
> ptep = lookup_address(address, &level);
> @@ -888,13 +886,6 @@ int m2p_add_override(unsigned long mfn, struct page *page,
> "m2p_add_override: pfn %lx not mapped", pfn))
> return -EINVAL;
> }
> - WARN_ON(PagePrivate(page));
> - SetPagePrivate(page);
> - set_page_private(page, mfn);
> - page->index = pfn_to_mfn(pfn);
> -
> - if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
> - return -ENOMEM;
>
> if (kmap_op != NULL) {
> if (!PageHighMem(page)) {
> @@ -933,20 +924,15 @@ int m2p_add_override(unsigned long mfn, struct page *page,
> }
> EXPORT_SYMBOL_GPL(m2p_add_override);
> int m2p_remove_override(struct page *page,
> - struct gnttab_map_grant_ref *kmap_op)
> + struct gnttab_map_grant_ref *kmap_op,
> + unsigned long pfn,
> + unsigned long mfn)
> {
> unsigned long flags;
> - unsigned long mfn;
> - unsigned long pfn;
> unsigned long uninitialized_var(address);
> unsigned level;
> pte_t *ptep = NULL;
>
> - pfn = page_to_pfn(page);
> - mfn = get_phys_to_machine(pfn);
> - if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT))
> - return -EINVAL;
> -
> if (!PageHighMem(page)) {
> address = (unsigned long)__va(pfn << PAGE_SHIFT);
> ptep = lookup_address(address, &level);
> @@ -959,10 +945,7 @@ int m2p_remove_override(struct page *page,
> spin_lock_irqsave(&m2p_override_lock, flags);
> list_del(&page->lru);
> spin_unlock_irqrestore(&m2p_override_lock, flags);
> - WARN_ON(!PagePrivate(page));
> - ClearPagePrivate(page);
>
> - set_phys_to_machine(pfn, page->index);
> if (kmap_op != NULL) {
> if (!PageHighMem(page)) {
> struct multicall_space mcs;
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 6620b73..875025f 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -285,8 +285,7 @@ static void free_persistent_gnts(struct xen_blkif *blkif, struct rb_root *root,
>
> if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST ||
> !rb_next(&persistent_gnt->node)) {
> - ret = gnttab_unmap_refs(unmap, NULL, pages,
> - segs_to_unmap);
> + ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
> BUG_ON(ret);
> put_free_pages(blkif, pages, segs_to_unmap);
> segs_to_unmap = 0;
> @@ -321,8 +320,7 @@ static void unmap_purged_grants(struct work_struct *work)
> pages[segs_to_unmap] = persistent_gnt->page;
>
> if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
> - ret = gnttab_unmap_refs(unmap, NULL, pages,
> - segs_to_unmap);
> + ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
> BUG_ON(ret);
> put_free_pages(blkif, pages, segs_to_unmap);
> segs_to_unmap = 0;
> @@ -330,7 +328,7 @@ static void unmap_purged_grants(struct work_struct *work)
> kfree(persistent_gnt);
> }
> if (segs_to_unmap > 0) {
> - ret = gnttab_unmap_refs(unmap, NULL, pages, segs_to_unmap);
> + ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
> BUG_ON(ret);
> put_free_pages(blkif, pages, segs_to_unmap);
> }
> @@ -670,15 +668,14 @@ static void xen_blkbk_unmap(struct xen_blkif *blkif,
> GNTMAP_host_map, pages[i]->handle);
> pages[i]->handle = BLKBACK_INVALID_HANDLE;
> if (++invcount == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
> - ret = gnttab_unmap_refs(unmap, NULL, unmap_pages,
> - invcount);
> + ret = gnttab_unmap_refs(unmap, unmap_pages, invcount);
> BUG_ON(ret);
> put_free_pages(blkif, unmap_pages, invcount);
> invcount = 0;
> }
> }
> if (invcount) {
> - ret = gnttab_unmap_refs(unmap, NULL, unmap_pages, invcount);
> + ret = gnttab_unmap_refs(unmap, unmap_pages, invcount);
> BUG_ON(ret);
> put_free_pages(blkif, unmap_pages, invcount);
> }
> @@ -740,7 +737,7 @@ again:
> }
>
> if (segs_to_map) {
> - ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
> + ret = gnttab_map_refs(map, pages_to_gnt, segs_to_map);
> BUG_ON(ret);
> }
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index e41c79c..e652c0e 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -284,8 +284,10 @@ static int map_grant_pages(struct grant_map *map)
> }
>
> pr_debug("map %d+%d\n", map->index, map->count);
> - err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
> - map->pages, map->count);
> + err = gnttab_map_refs_userspace(map->map_ops,
> + use_ptemod ? map->kmap_ops : NULL,
> + map->pages,
> + map->count);
> if (err)
> return err;
>
> @@ -315,9 +317,10 @@ static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
> }
> }
>
> - err = gnttab_unmap_refs(map->unmap_ops + offset,
> - use_ptemod ? map->kmap_ops + offset : NULL, map->pages + offset,
> - pages);
> + err = gnttab_unmap_refs_userspace(map->unmap_ops + offset,
> + use_ptemod ? map->kmap_ops + offset : NULL,
> + map->pages + offset,
> + pages);
> if (err)
> return err;
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index aa846a4..2add483 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -880,15 +880,17 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
> }
> EXPORT_SYMBOL_GPL(gnttab_batch_copy);
>
> -int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> +int __gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> struct gnttab_map_grant_ref *kmap_ops,
> - struct page **pages, unsigned int count)
> + struct page **pages, unsigned int count,
> + bool m2p_override)
> {
> int i, ret;
> bool lazy = false;
> pte_t *pte;
> - unsigned long mfn;
> + unsigned long mfn, pfn;
>
> + BUG_ON(kmap_ops && !m2p_override);
> ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
> if (ret)
> return ret;
> @@ -907,10 +909,12 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> set_phys_to_machine(map_ops[i].host_addr >> PAGE_SHIFT,
> map_ops[i].dev_bus_addr >> PAGE_SHIFT);
> }
> - return ret;
> + return 0;
> }
>
> - if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> + if (m2p_override &&
> + !in_interrupt() &&
> + paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> arch_enter_lazy_mmu_mode();
> lazy = true;
> }
> @@ -927,8 +931,20 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> } else {
> mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
> }
> - ret = m2p_add_override(mfn, pages[i], kmap_ops ?
> - &kmap_ops[i] : NULL);
> + pfn = page_to_pfn(pages[i]);
> +
> + WARN_ON(PagePrivate(pages[i]));
> + SetPagePrivate(pages[i]);
> + set_page_private(pages[i], mfn);
> +
> + pages[i]->index = pfn_to_mfn(pfn);
> + if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)))) {
> + ret = -ENOMEM;
> + goto out;
> + }
> + if (m2p_override)
> + ret = m2p_add_override(mfn, pages[i], kmap_ops ?
> + &kmap_ops[i] : NULL, pfn);
> if (ret)
> goto out;
> }
> @@ -939,15 +955,32 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>
> return ret;
> }
> +
> +int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> + struct page **pages, unsigned int count)
> +{
> + return __gnttab_map_refs(map_ops, NULL, pages, count, false);
> +}
> EXPORT_SYMBOL_GPL(gnttab_map_refs);
>
> -int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
> +int gnttab_map_refs_userspace(struct gnttab_map_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> + struct page **pages, unsigned int count)
> +{
> + return __gnttab_map_refs(map_ops, kmap_ops, pages, count, true);
> +}
> +EXPORT_SYMBOL_GPL(gnttab_map_refs_userspace);
> +
> +int __gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
> struct gnttab_map_grant_ref *kmap_ops,
> - struct page **pages, unsigned int count)
> + struct page **pages, unsigned int count,
> + bool m2p_override)
> {
> int i, ret;
> bool lazy = false;
> + unsigned long pfn, mfn;
>
> + BUG_ON(kmap_ops && !m2p_override);
> ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
> if (ret)
> return ret;
> @@ -958,17 +991,34 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
> set_phys_to_machine(unmap_ops[i].host_addr >> PAGE_SHIFT,
> INVALID_P2M_ENTRY);
> }
> - return ret;
> + return 0;
> }
>
> - if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> + if (m2p_override &&
> + !in_interrupt() &&
> + paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> arch_enter_lazy_mmu_mode();
> lazy = true;
> }
>
> for (i = 0; i < count; i++) {
> - ret = m2p_remove_override(pages[i], kmap_ops ?
> - &kmap_ops[i] : NULL);
> + pfn = page_to_pfn(pages[i]);
> + mfn = get_phys_to_machine(pfn);
> + if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT)) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + set_page_private(pages[i], INVALID_P2M_ENTRY);
> + WARN_ON(!PagePrivate(pages[i]));
> + ClearPagePrivate(pages[i]);
> + set_phys_to_machine(pfn, pages[i]->index);
> + if (m2p_override)
> + ret = m2p_remove_override(pages[i],
> + kmap_ops ?
> + &kmap_ops[i] : NULL,
> + pfn,
> + mfn);
> if (ret)
> goto out;
> }
> @@ -979,8 +1029,22 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
>
> return ret;
> }
> +
> +int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *map_ops,
> + struct page **pages, unsigned int count)
> +{
> + return __gnttab_unmap_refs(map_ops, NULL, pages, count, false);
> +}
> EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
>
> +int gnttab_unmap_refs_userspace(struct gnttab_unmap_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> + struct page **pages, unsigned int count)
> +{
> + return __gnttab_unmap_refs(map_ops, kmap_ops, pages, count, true);
> +}
> +EXPORT_SYMBOL_GPL(gnttab_unmap_refs_userspace);
> +
> static unsigned nr_status_frames(unsigned nr_grant_frames)
> {
> BUG_ON(grefs_per_grant_frame == 0);
> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
> index 694dcaf..9a919b1 100644
> --- a/include/xen/grant_table.h
> +++ b/include/xen/grant_table.h
> @@ -184,11 +184,15 @@ 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_map_refs_userspace(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 gnttab_map_grant_ref *kunmap_ops,
> struct page **pages, unsigned int count);
> +int gnttab_unmap_refs_userspace(struct gnttab_unmap_grant_ref *unmap_ops,
> + struct gnttab_map_grant_ref *kunmap_ops,
> + struct page **pages, unsigned int count);
>
> /* Perform a batch of grant map/copy operations. Retry every batch slot
> * for which the hypervisor returns GNTST_eagain. This is typically due
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
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