| Message ID | 20220517090529.3140417-5-Penny.Zheng@arm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | static shared memory on dom0less system | expand |
On Tue, 17 May 2022, Penny Zheng wrote: > Later, we need to add the right amount of references, which should be > the number of borrower domains, to the owner domain. Since we only have > get_page() to increment the page reference by 1, a loop is needed per > page, which is inefficient and time-consuming. > > To save the loop time, this commit introduces a set of new helpers > put_page_nr() and get_page_nr() to increment/drop the page reference by nr. > > Signed-off-by: Penny Zheng <penny.zheng@arm.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org> > --- > v4 changes: > - make sure that the right equation return is at least equal to n > - simplify the underflow > --- > v3 changes: > - check overflow with "n" > - remove spurious change > - bring back the check that we enter the loop only when count_info is > greater than 0 > --- > v2 change: > - new commit > --- > xen/arch/arm/include/asm/mm.h | 4 ++++ > xen/arch/arm/mm.c | 42 +++++++++++++++++++++++++++-------- > 2 files changed, 37 insertions(+), 9 deletions(-) > > diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h > index 424aaf2823..c737d51e4d 100644 > --- a/xen/arch/arm/include/asm/mm.h > +++ b/xen/arch/arm/include/asm/mm.h > @@ -347,6 +347,10 @@ void free_init_memory(void); > int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn, > unsigned int order); > > +extern bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr); > +extern void put_page_nr(struct page_info *page, unsigned long nr); > + > extern void put_page_type(struct page_info *page); > static inline void put_page_and_type(struct page_info *page) > { > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c > index 7b1f2f4906..8c8a8f6378 100644 > --- a/xen/arch/arm/mm.c > +++ b/xen/arch/arm/mm.c > @@ -1537,21 +1537,29 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg) > return 0; > } > > -struct domain *page_get_owner_and_reference(struct page_info *page) > +static struct domain *page_get_owner_and_nr_reference(struct page_info *page, > + unsigned long nr) > { > unsigned long x, y = page->count_info; > struct domain *owner; > > + /* Restrict nr to avoid "double" overflow */ > + if ( nr >= PGC_count_mask ) > + { > + ASSERT_UNREACHABLE(); > + return NULL; > + } > + > do { > x = y; > /* > * Count == 0: Page is not allocated, so we cannot take a reference. > * Count == -1: Reference count would wrap, which is invalid. > */ > - if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) > + if ( unlikely(((x + nr) & PGC_count_mask) <= nr) ) > return NULL; > } > - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); > + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); > > owner = page_get_owner(page); > ASSERT(owner); > @@ -1559,14 +1567,19 @@ struct domain *page_get_owner_and_reference(struct page_info *page) > return owner; > } > > -void put_page(struct page_info *page) > +struct domain *page_get_owner_and_reference(struct page_info *page) > +{ > + return page_get_owner_and_nr_reference(page, 1); > +} > + > +void put_page_nr(struct page_info *page, unsigned long nr) > { > unsigned long nx, x, y = page->count_info; > > do { > - ASSERT((y & PGC_count_mask) != 0); > + ASSERT((y & PGC_count_mask) >= nr); > x = y; > - nx = x - 1; > + nx = x - nr; > } > while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); > > @@ -1576,19 +1589,30 @@ void put_page(struct page_info *page) > } > } > > -bool get_page(struct page_info *page, const struct domain *domain) > +void put_page(struct page_info *page) > +{ > + put_page_nr(page, 1); > +} > + > +bool get_page_nr(struct page_info *page, const struct domain *domain, > + unsigned long nr) > { > - const struct domain *owner = page_get_owner_and_reference(page); > + const struct domain *owner = page_get_owner_and_nr_reference(page, nr); > > if ( likely(owner == domain) ) > return true; > > if ( owner != NULL ) > - put_page(page); > + put_page_nr(page, nr); > > return false; > } > > +bool get_page(struct page_info *page, const struct domain *domain) > +{ > + return get_page_nr(page, domain, 1); > +} > + > /* Common code requires get_page_type and put_page_type. > * We don't care about typecounts so we just do the minimum to make it > * happy. */ > -- > 2.25.1 >
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h index 424aaf2823..c737d51e4d 100644 --- a/xen/arch/arm/include/asm/mm.h +++ b/xen/arch/arm/include/asm/mm.h @@ -347,6 +347,10 @@ void free_init_memory(void); int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn, unsigned int order); +extern bool get_page_nr(struct page_info *page, const struct domain *domain, + unsigned long nr); +extern void put_page_nr(struct page_info *page, unsigned long nr); + extern void put_page_type(struct page_info *page); static inline void put_page_and_type(struct page_info *page) { diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 7b1f2f4906..8c8a8f6378 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -1537,21 +1537,29 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg) return 0; } -struct domain *page_get_owner_and_reference(struct page_info *page) +static struct domain *page_get_owner_and_nr_reference(struct page_info *page, + unsigned long nr) { unsigned long x, y = page->count_info; struct domain *owner; + /* Restrict nr to avoid "double" overflow */ + if ( nr >= PGC_count_mask ) + { + ASSERT_UNREACHABLE(); + return NULL; + } + do { x = y; /* * Count == 0: Page is not allocated, so we cannot take a reference. * Count == -1: Reference count would wrap, which is invalid. */ - if ( unlikely(((x + 1) & PGC_count_mask) <= 1) ) + if ( unlikely(((x + nr) & PGC_count_mask) <= nr) ) return NULL; } - while ( (y = cmpxchg(&page->count_info, x, x + 1)) != x ); + while ( (y = cmpxchg(&page->count_info, x, x + nr)) != x ); owner = page_get_owner(page); ASSERT(owner); @@ -1559,14 +1567,19 @@ struct domain *page_get_owner_and_reference(struct page_info *page) return owner; } -void put_page(struct page_info *page) +struct domain *page_get_owner_and_reference(struct page_info *page) +{ + return page_get_owner_and_nr_reference(page, 1); +} + +void put_page_nr(struct page_info *page, unsigned long nr) { unsigned long nx, x, y = page->count_info; do { - ASSERT((y & PGC_count_mask) != 0); + ASSERT((y & PGC_count_mask) >= nr); x = y; - nx = x - 1; + nx = x - nr; } while ( unlikely((y = cmpxchg(&page->count_info, x, nx)) != x) ); @@ -1576,19 +1589,30 @@ void put_page(struct page_info *page) } } -bool get_page(struct page_info *page, const struct domain *domain) +void put_page(struct page_info *page) +{ + put_page_nr(page, 1); +} + +bool get_page_nr(struct page_info *page, const struct domain *domain, + unsigned long nr) { - const struct domain *owner = page_get_owner_and_reference(page); + const struct domain *owner = page_get_owner_and_nr_reference(page, nr); if ( likely(owner == domain) ) return true; if ( owner != NULL ) - put_page(page); + put_page_nr(page, nr); return false; } +bool get_page(struct page_info *page, const struct domain *domain) +{ + return get_page_nr(page, domain, 1); +} + /* Common code requires get_page_type and put_page_type. * We don't care about typecounts so we just do the minimum to make it * happy. */
Later, we need to add the right amount of references, which should be the number of borrower domains, to the owner domain. Since we only have get_page() to increment the page reference by 1, a loop is needed per page, which is inefficient and time-consuming. To save the loop time, this commit introduces a set of new helpers put_page_nr() and get_page_nr() to increment/drop the page reference by nr. Signed-off-by: Penny Zheng <penny.zheng@arm.com> --- v4 changes: - make sure that the right equation return is at least equal to n - simplify the underflow --- v3 changes: - check overflow with "n" - remove spurious change - bring back the check that we enter the loop only when count_info is greater than 0 --- v2 change: - new commit --- xen/arch/arm/include/asm/mm.h | 4 ++++ xen/arch/arm/mm.c | 42 +++++++++++++++++++++++++++-------- 2 files changed, 37 insertions(+), 9 deletions(-)