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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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