| Message ID | 20190916153504.30809-1-billodo@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xfs: assure zeroed memory buffers for certain kmem allocations | expand |
On 9/16/19 10:35 AM, Bill O'Donnell wrote: > Guarantee zeroed memory buffers for cases where potential memory > leak to disk can occur. In these cases, kmem_alloc is used and > doesn't zero the buffer, opening the possibility of information > leakage to disk. > > Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > obtain the already zeroed buffer from kernel memory. > > This solution avoids the performance issue that would occur if a > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> I think this can probably be further optimized by not obtaining zeroed memory when we're about to fill the buffer from disk as the very next step. (in this case, xfs_buf_read_map calls xfs_buf_get_map and then immediately reads the buffer from disk with _xfs_buf_read) xfs_buf_read_map adds XBF_READ to the flags during this process. So I wonder if this can be simplified/optimized by just checking for XBF_READ in xfs_buf_allocate_memory's flags, and if it's not set, then request zeroed memory, because that indicates a buffer we'll be filling in from memory and subsequently writing to disk. -Eric > --- > fs/xfs/xfs_buf.c | 8 ++++++-- > fs/xfs/xfs_buf.h | 4 +++- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 120ef99d09e8..916a3f782950 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( > unsigned short page_count, i; > xfs_off_t start, end; > int error; > + uint kmflag_mask = 0; > > /* > * for buffers that are contained within a single page, just allocate > * the memory from the heap - there's no need for the complexity of > * page arrays to keep allocation down to order 0. > */ > + if (flags & _XBF_KMZ) > + kmflag_mask |= KM_ZERO; > size = BBTOB(bp->b_length); > if (size < PAGE_SIZE) { > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); > if (!bp->b_addr) { > /* low memory - use alloc_page loop instead */ > goto use_alloc_page; > @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( > struct page *page; > uint retries = 0; > retry: > - page = alloc_page(gfp_mask); > + page = alloc_page(gfp_mask | kmflag_mask); > if (unlikely(page == NULL)) { > if (flags & XBF_READ_AHEAD) { > bp->b_page_count = i; > @@ -683,6 +686,7 @@ xfs_buf_get_map( > struct xfs_buf *new_bp; > int error = 0; > > + flags |= _XBF_KMZ; > error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); > > switch (error) { > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > index f6ce17d8d848..416ff588240a 100644 > --- a/fs/xfs/xfs_buf.h > +++ b/fs/xfs/xfs_buf.h > @@ -38,6 +38,7 @@ > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > #define _XBF_KMEM (1 << 21)/* backed by heap memory */ > #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ > +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ > > typedef unsigned int xfs_buf_flags_t; > > @@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t; > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > { _XBF_PAGES, "PAGES" }, \ > { _XBF_KMEM, "KMEM" }, \ > - { _XBF_DELWRI_Q, "DELWRI_Q" } > + { _XBF_DELWRI_Q, "DELWRI_Q" }, \ > + { _XBF_KMZ, "KMEM_Z" } > > > /* >
On Mon, Sep 16, 2019 at 04:24:40PM -0500, Eric Sandeen wrote: > On 9/16/19 10:35 AM, Bill O'Donnell wrote: > > Guarantee zeroed memory buffers for cases where potential memory > > leak to disk can occur. In these cases, kmem_alloc is used and > > doesn't zero the buffer, opening the possibility of information > > leakage to disk. > > > > Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed > > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > > obtain the already zeroed buffer from kernel memory. > > > > This solution avoids the performance issue that would occur if a > > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> > > I think this can probably be further optimized by not obtaining zeroed > memory when we're about to fill the buffer from disk as the very > next step. > > (in this case, xfs_buf_read_map calls xfs_buf_get_map and then immediately > reads the buffer from disk with _xfs_buf_read) xfs_buf_read_map adds > XBF_READ to the flags during this process. > > So I wonder if this can be simplified/optimized by just checking for XBF_READ > in xfs_buf_allocate_memory's flags, and if it's not set, then request > zeroed memory, because that indicates a buffer we'll be filling in from > memory and subsequently writing to disk. I was wondering that ("Why can't we allocate a zeroed buffer only for the get_buf case so that we don't have to do that for the read_buf case?") too. Once you do that then you can then remove all the explicit memset calls too. > -Eric > > > --- > > fs/xfs/xfs_buf.c | 8 ++++++-- > > fs/xfs/xfs_buf.h | 4 +++- > > 2 files changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index 120ef99d09e8..916a3f782950 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( > > unsigned short page_count, i; > > xfs_off_t start, end; > > int error; > > + uint kmflag_mask = 0; > > > > /* > > * for buffers that are contained within a single page, just allocate > > * the memory from the heap - there's no need for the complexity of > > * page arrays to keep allocation down to order 0. > > */ > > + if (flags & _XBF_KMZ) > > + kmflag_mask |= KM_ZERO; > > size = BBTOB(bp->b_length); > > if (size < PAGE_SIZE) { > > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > > + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); Does this overflow 80 columns? --D > > if (!bp->b_addr) { > > /* low memory - use alloc_page loop instead */ > > goto use_alloc_page; > > @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( > > struct page *page; > > uint retries = 0; > > retry: > > - page = alloc_page(gfp_mask); > > + page = alloc_page(gfp_mask | kmflag_mask); > > if (unlikely(page == NULL)) { > > if (flags & XBF_READ_AHEAD) { > > bp->b_page_count = i; > > @@ -683,6 +686,7 @@ xfs_buf_get_map( > > struct xfs_buf *new_bp; > > int error = 0; > > > > + flags |= _XBF_KMZ; > > error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); > > > > switch (error) { > > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > > index f6ce17d8d848..416ff588240a 100644 > > --- a/fs/xfs/xfs_buf.h > > +++ b/fs/xfs/xfs_buf.h > > @@ -38,6 +38,7 @@ > > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > > #define _XBF_KMEM (1 << 21)/* backed by heap memory */ > > #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ > > +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ > > > > typedef unsigned int xfs_buf_flags_t; > > > > @@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t; > > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > > { _XBF_PAGES, "PAGES" }, \ > > { _XBF_KMEM, "KMEM" }, \ > > - { _XBF_DELWRI_Q, "DELWRI_Q" } > > + { _XBF_DELWRI_Q, "DELWRI_Q" }, \ > > + { _XBF_KMZ, "KMEM_Z" } > > > > > > /* > >
On Mon, Sep 16, 2019 at 04:24:40PM -0500, Eric Sandeen wrote: > On 9/16/19 10:35 AM, Bill O'Donnell wrote: > > Guarantee zeroed memory buffers for cases where potential memory > > leak to disk can occur. In these cases, kmem_alloc is used and > > doesn't zero the buffer, opening the possibility of information > > leakage to disk. > > > > Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed > > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > > obtain the already zeroed buffer from kernel memory. > > > > This solution avoids the performance issue that would occur if a > > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> > > I think this can probably be further optimized by not obtaining zeroed > memory when we're about to fill the buffer from disk as the very > next step. Yep. I missed that redundancy. > > (in this case, xfs_buf_read_map calls xfs_buf_get_map and then immediately > reads the buffer from disk with _xfs_buf_read) xfs_buf_read_map adds > XBF_READ to the flags during this process. > > So I wonder if this can be simplified/optimized by just checking for XBF_READ > in xfs_buf_allocate_memory's flags, and if it's not set, then request > zeroed memory, because that indicates a buffer we'll be filling in from > memory and subsequently writing to disk. nod. > > -Eric > > > --- > > fs/xfs/xfs_buf.c | 8 ++++++-- > > fs/xfs/xfs_buf.h | 4 +++- > > 2 files changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index 120ef99d09e8..916a3f782950 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( > > unsigned short page_count, i; > > xfs_off_t start, end; > > int error; > > + uint kmflag_mask = 0; > > > > /* > > * for buffers that are contained within a single page, just allocate > > * the memory from the heap - there's no need for the complexity of > > * page arrays to keep allocation down to order 0. > > */ > > + if (flags & _XBF_KMZ) > > + kmflag_mask |= KM_ZERO; > > size = BBTOB(bp->b_length); > > if (size < PAGE_SIZE) { > > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > > + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); > > if (!bp->b_addr) { > > /* low memory - use alloc_page loop instead */ > > goto use_alloc_page; > > @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( > > struct page *page; > > uint retries = 0; > > retry: > > - page = alloc_page(gfp_mask); > > + page = alloc_page(gfp_mask | kmflag_mask); > > if (unlikely(page == NULL)) { > > if (flags & XBF_READ_AHEAD) { > > bp->b_page_count = i; > > @@ -683,6 +686,7 @@ xfs_buf_get_map( > > struct xfs_buf *new_bp; > > int error = 0; > > > > + flags |= _XBF_KMZ; > > error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); > > > > switch (error) { > > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > > index f6ce17d8d848..416ff588240a 100644 > > --- a/fs/xfs/xfs_buf.h > > +++ b/fs/xfs/xfs_buf.h > > @@ -38,6 +38,7 @@ > > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > > #define _XBF_KMEM (1 << 21)/* backed by heap memory */ > > #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ > > +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ > > > > typedef unsigned int xfs_buf_flags_t; > > > > @@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t; > > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > > { _XBF_PAGES, "PAGES" }, \ > > { _XBF_KMEM, "KMEM" }, \ > > - { _XBF_DELWRI_Q, "DELWRI_Q" } > > + { _XBF_DELWRI_Q, "DELWRI_Q" }, \ > > + { _XBF_KMZ, "KMEM_Z" } > > > > > > /* > >
On Mon, Sep 16, 2019 at 10:35:04AM -0500, Bill O'Donnell wrote: > Guarantee zeroed memory buffers for cases where potential memory > leak to disk can occur. In these cases, kmem_alloc is used and > doesn't zero the buffer, opening the possibility of information > leakage to disk. > > Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > obtain the already zeroed buffer from kernel memory. > > This solution avoids the performance issue that would occur if a > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > Signed-off-by: Bill O'Donnell <billodo@redhat.com> > --- > fs/xfs/xfs_buf.c | 8 ++++++-- > fs/xfs/xfs_buf.h | 4 +++- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 120ef99d09e8..916a3f782950 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( > unsigned short page_count, i; > xfs_off_t start, end; > int error; > + uint kmflag_mask = 0; > > /* > * for buffers that are contained within a single page, just allocate > * the memory from the heap - there's no need for the complexity of > * page arrays to keep allocation down to order 0. > */ > + if (flags & _XBF_KMZ) > + kmflag_mask |= KM_ZERO; > size = BBTOB(bp->b_length); > if (size < PAGE_SIZE) { > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); > if (!bp->b_addr) { > /* low memory - use alloc_page loop instead */ > goto use_alloc_page; > @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( > struct page *page; > uint retries = 0; > retry: > - page = alloc_page(gfp_mask); > + page = alloc_page(gfp_mask | kmflag_mask); > if (unlikely(page == NULL)) { > if (flags & XBF_READ_AHEAD) { > bp->b_page_count = i; > @@ -683,6 +686,7 @@ xfs_buf_get_map( > struct xfs_buf *new_bp; > int error = 0; > > + flags |= _XBF_KMZ; > error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); IIRC, this flag was supposed to go into xfs_trans_get_buf_map() and direct callers of xfs_buf_get*() that weren't in the read path. That avoids the need for zeroing pages that we are going to DMA actual data into before it gets to users... > switch (error) { > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > index f6ce17d8d848..416ff588240a 100644 > --- a/fs/xfs/xfs_buf.h > +++ b/fs/xfs/xfs_buf.h > @@ -38,6 +38,7 @@ > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > #define _XBF_KMEM (1 << 21)/* backed by heap memory */ > #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ > +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ "KMZ" isn't very descriptive, and it shouldn't have a "_" prefix as it's not internal to the buffer cache - it's a caller controlled flag like XBF_TRYLOCK. I'd suggest something like XBF_INIT_PAGES or XBF_ZERO to make it clear we are asking for ithe buffer to be explicitly initialised to zero. Cheers, Dave.
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 120ef99d09e8..916a3f782950 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( unsigned short page_count, i; xfs_off_t start, end; int error; + uint kmflag_mask = 0; /* * for buffers that are contained within a single page, just allocate * the memory from the heap - there's no need for the complexity of * page arrays to keep allocation down to order 0. */ + if (flags & _XBF_KMZ) + kmflag_mask |= KM_ZERO; size = BBTOB(bp->b_length); if (size < PAGE_SIZE) { int align_mask = xfs_buftarg_dma_alignment(bp->b_target); - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); if (!bp->b_addr) { /* low memory - use alloc_page loop instead */ goto use_alloc_page; @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( struct page *page; uint retries = 0; retry: - page = alloc_page(gfp_mask); + page = alloc_page(gfp_mask | kmflag_mask); if (unlikely(page == NULL)) { if (flags & XBF_READ_AHEAD) { bp->b_page_count = i; @@ -683,6 +686,7 @@ xfs_buf_get_map( struct xfs_buf *new_bp; int error = 0; + flags |= _XBF_KMZ; error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); switch (error) { diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h index f6ce17d8d848..416ff588240a 100644 --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h @@ -38,6 +38,7 @@ #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ #define _XBF_KMEM (1 << 21)/* backed by heap memory */ #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ typedef unsigned int xfs_buf_flags_t; @@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t; { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ { _XBF_PAGES, "PAGES" }, \ { _XBF_KMEM, "KMEM" }, \ - { _XBF_DELWRI_Q, "DELWRI_Q" } + { _XBF_DELWRI_Q, "DELWRI_Q" }, \ + { _XBF_KMZ, "KMEM_Z" } /*
Guarantee zeroed memory buffers for cases where potential memory leak to disk can occur. In these cases, kmem_alloc is used and doesn't zero the buffer, opening the possibility of information leakage to disk. Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed buffer, and use existing infrastucture (xfs_buf_allocate_memory) to obtain the already zeroed buffer from kernel memory. This solution avoids the performance issue that would occur if a wholesale change to replace kmem_alloc with kmem_zalloc was done. Signed-off-by: Bill O'Donnell <billodo@redhat.com> --- fs/xfs/xfs_buf.c | 8 ++++++-- fs/xfs/xfs_buf.h | 4 +++- 2 files changed, 9 insertions(+), 3 deletions(-)