Call VM_BUG_ON() if offset + len > PAGE_SIZE.
This is an RFC patch because I'm not sure if we actually need to BUG_ON(),
so I'd like to know what Maintainers and other developers think about this
proposal.
Please note that memset_page() uses VM_BUG_ON() to prevent the same issue.
Furthermore, I also cannot understand why memset_page() does not call
flush_dcache_page() after memset() but I suppose that the different
implementations of these two functions should be addressed in another RFC.
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
include/linux/highmem.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index c3d562b5f0c1..bdb16d5f8148 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -349,6 +349,8 @@ static inline void memcpy_to_page(struct page *page, size_t offset,
static inline void memzero_page(struct page *page, size_t offset, size_t len)
{
char *addr = kmap_local_page(page);
+
+ VM_BUG_ON(offset + len > PAGE_SIZE);
memset(addr + offset, 0, len);
flush_dcache_page(page);
kunmap_local(addr);
--
2.34.1
On domenica 24 aprile 2022 12:48:06 CEST Fabio M. De Francesco wrote:
> Call VM_BUG_ON() if offset + len > PAGE_SIZE.
>
> This is an RFC patch because I'm not sure if we actually need to
BUG_ON(),
Actually I considered VM_BUG_ON() for consistency with the other functions
in highmem.h
What about VM_WARN_ON_ONCE() here and also in memset_page?
Thanks,
Fabio
> so I'd like to know what Maintainers and other developers think about
this
> proposal.
>
> Please note that memset_page() uses VM_BUG_ON() to prevent the same
issue.
>
> Furthermore, I also cannot understand why memset_page() does not call
> flush_dcache_page() after memset() but I suppose that the different
> implementations of these two functions should be addressed in another
RFC.
>
> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
> include/linux/highmem.h | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index c3d562b5f0c1..bdb16d5f8148 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -349,6 +349,8 @@ static inline void memcpy_to_page(struct page *page,
size_t offset,
> static inline void memzero_page(struct page *page, size_t offset, size_t
len)
> {
> char *addr = kmap_local_page(page);
> +
> + VM_BUG_ON(offset + len > PAGE_SIZE);
> memset(addr + offset, 0, len);
> flush_dcache_page(page);
> kunmap_local(addr);
> --
> 2.34.1
>
>
On Mon, Apr 25, 2022 at 03:47:38AM +0200, Fabio M. De Francesco wrote:
> On domenica 24 aprile 2022 12:48:06 CEST Fabio M. De Francesco wrote:
> > Call VM_BUG_ON() if offset + len > PAGE_SIZE.
> >
> > This is an RFC patch because I'm not sure if we actually need to
> BUG_ON(),
>
> Actually I considered VM_BUG_ON() for consistency with the other functions
> in highmem.h
>
> What about VM_WARN_ON_ONCE() here and also in memset_page?
For consistency leave this as a VM_BUG_ON[1]
I've been down a similar path[2] and there was a long discussion about it.[3]
In the end we settled on VM_BUG_ON.[4]
As to the addition of flush_dcache_page(). There was a discussion here.
https://lore.kernel.org/lkml/CAHk-=wiKac4t-fOP_3fAf7nETfFLhT3ShmRmBq2J96y6jAr56Q@mail.gmail.com/
Ira
[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/[email protected]/
[3] https://lore.kernel.org/lkml/[email protected]/
[4] https://lore.kernel.org/lkml/[email protected]/
>
> Thanks,
>
> Fabio
>
> > so I'd like to know what Maintainers and other developers think about
> this
> > proposal.
> >
> > Please note that memset_page() uses VM_BUG_ON() to prevent the same
> issue.
> >
> > Furthermore, I also cannot understand why memset_page() does not call
> > flush_dcache_page() after memset() but I suppose that the different
> > implementations of these two functions should be addressed in another
> RFC.
> >
> > Signed-off-by: Fabio M. De Francesco <[email protected]>
> > ---
> > include/linux/highmem.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> > index c3d562b5f0c1..bdb16d5f8148 100644
> > --- a/include/linux/highmem.h
> > +++ b/include/linux/highmem.h
> > @@ -349,6 +349,8 @@ static inline void memcpy_to_page(struct page *page,
> size_t offset,
> > static inline void memzero_page(struct page *page, size_t offset, size_t
> len)
> > {
> > char *addr = kmap_local_page(page);
> > +
> > + VM_BUG_ON(offset + len > PAGE_SIZE);
> > memset(addr + offset, 0, len);
> > flush_dcache_page(page);
> > kunmap_local(addr);
> > --
> > 2.34.1
> >
> >
>
>
>
>
On lunedì 25 aprile 2022 18:47:18 CEST Ira Weiny wrote:
> On Mon, Apr 25, 2022 at 03:47:38AM +0200, Fabio M. De Francesco wrote:
> > On domenica 24 aprile 2022 12:48:06 CEST Fabio M. De Francesco wrote:
> > > Call VM_BUG_ON() if offset + len > PAGE_SIZE.
> > >
> > > This is an RFC patch because I'm not sure if we actually need to
> > BUG_ON(),
> >
> > Actually I considered VM_BUG_ON() for consistency with the other
functions
> > in highmem.h
> >
> > What about VM_WARN_ON_ONCE() here and also in memset_page?
>
> For consistency leave this as a VM_BUG_ON[1]
>
> I've been down a similar path[2] and there was a long discussion about
it.[3]
>
> In the end we settled on VM_BUG_ON.[4]
Thanks for your reply and for providing so many helpful links :)
I just read the ones related to VM_BUG_ON() (I don't have time for
flush_dcache_page() today). Since the consensus for these kinds of issues
is in favor of using VM_BUG_ON(), that's OK for me.
I will send a "real" patch by tomorrow.
Again, thanks,
Fabio
> As to the addition of flush_dcache_page(). There was a discussion here.
>
> https://lore.kernel.org/lkml/CAHk-=wiKac4t-fOP_3fAf7nETfFLhT3ShmRmBq2J96y6jAr56Q@mail.gmail.com/
>
> Ira
>
> [1] https://lore.kernel.org/lkml/[email protected]/
>
> [2] https://lore.kernel.org/lkml/[email protected]/
>
> [3] https://lore.kernel.org/lkml/[email protected]/
>
> [4] https://lore.kernel.org/lkml/[email protected]/