On Wed, Feb 28, 2024 at 02:28:45PM +0100, Paolo Bonzini wrote:
> On Wed, Feb 28, 2024 at 2:15 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> >
> > On Tue, Feb 27, 2024 at 06:17:34PM -0800, Yosry Ahmed wrote:
> > > On Tue, Feb 27, 2024 at 6:15 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > > >
> > > > On Tue, Feb 27, 2024, Paolo Bonzini wrote:
> > > >
> > > > This needs a changelog, and also needs to be Cc'd to someone(s) that can give it
> > > > a thumbs up.
> > >
> > > +Matthew Wilcox
> >
> > If only there were an entry in MAINTAINERS for filemap.c ...
>
> Not CCing you (or mm in general) was intentional because I first
> wanted a review of the KVM APIs; of course I wouldn't have committed
> it without an Acked-by. But yeah, not writing the changelog yet was
> pure laziness.
>
> Since you're here: KVM would like to add a ioctl to encrypt and
> install a page into guest_memfd, in preparation for launching an
> encrypted guest. For this API we want to rule out the possibility of
> overwriting a page that is already in the guest_memfd's filemap,
> therefore this API would pass FGP_CREAT_ONLY|FGP_CREAT
> into__filemap_get_folio. Do you think this is bogus...
>
> > This looks bogus to me, and if it's not bogus, it's incomplete.
>
> ... or if not, what incompleteness can you spot?
>
> Thanks,
>
> Paolo
>
> > But it's hard to judge without a commit message that describes what it's
> > supposed to mean.
> >
> > > >
> > > > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > > > ---
> > > > > include/linux/pagemap.h | 2 ++
> > > > > mm/filemap.c | 4 ++++
> > > > > 2 files changed, 6 insertions(+)
> > > > >
> > > > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > > > > index 2df35e65557d..e8ac0b32f84d 100644
> > > > > --- a/include/linux/pagemap.h
> > > > > +++ b/include/linux/pagemap.h
> > > > > @@ -586,6 +586,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
> > > > > * * %FGP_CREAT - If no folio is present then a new folio is allocated,
> > > > > * added to the page cache and the VM's LRU list. The folio is
> > > > > * returned locked.
> > > > > + * * %FGP_CREAT_ONLY - Fail if a folio is not present
^
So should be: Fail if a folio is present.
Thanks,
Yilun
> > > > > * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
> > > > > * folio is already in cache. If the folio was allocated, unlock it
> > > > > * before returning so the caller can do the same dance.
> > > > > @@ -606,6 +607,7 @@ typedef unsigned int __bitwise fgf_t;
> > > > > #define FGP_NOWAIT ((__force fgf_t)0x00000020)
> > > > > #define FGP_FOR_MMAP ((__force fgf_t)0x00000040)
> > > > > #define FGP_STABLE ((__force fgf_t)0x00000080)
> > > > > +#define FGP_CREAT_ONLY ((__force fgf_t)0x00000100)
> > > > > #define FGF_GET_ORDER(fgf) (((__force unsigned)fgf) >> 26) /* top 6 bits */
> > > > >
> > > > > #define FGP_WRITEBEGIN (FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE)
> > > > > diff --git a/mm/filemap.c b/mm/filemap.c
> > > > > index 750e779c23db..d5107bd0cd09 100644
> > > > > --- a/mm/filemap.c
> > > > > +++ b/mm/filemap.c
> > > > > @@ -1854,6 +1854,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> > > > > folio = NULL;
> > > > > if (!folio)
> > > > > goto no_page;
> > > > > + if (fgp_flags & FGP_CREAT_ONLY) {
> > > > > + folio_put(folio);
> > > > > + return ERR_PTR(-EEXIST);
> > > > > + }
> > > > >
> > > > > if (fgp_flags & FGP_LOCK) {
> > > > > if (fgp_flags & FGP_NOWAIT) {
> > > > > --
> > > > > 2.39.0
> > > > >
> > > > >
> > > >
> >
>
>
