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Date: Fri, 24 Jan 2014 14:48:58 +0000
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: Zoltan Kiss <zoltan.kiss@...rix.com>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
<david.vrabel@...rix.com>, <boris.ostrovsky@...cle.com>,
<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [Xen-devel] [PATCH v5] xen/grant-table: Avoid m2p_override during
mapping
On Fri, 24 Jan 2014, Konrad Rzeszutek Wilk wrote:
> 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@...rix.com>
> > Suggested-by: David Vrabel <david.vrabel@...rix.com>
>
> 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.
I reviewed-by the v6 version of the patch
> > 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@...ts.xen.org
> > http://lists.xen.org/xen-devel
>
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