On Wed, Feb 15, 2023, Oliver Upton wrote:
> On Wed, Feb 15, 2023 at 01:16:10AM +0000, Anish Moorthy wrote:
> > The upcoming mem_fault_nowait commits will make it so that, when the
> > relevant cap is enabled, hva_to_pfn will return after calling
> > hva_to_pfn_fast without ever attempting to pin memory via
> > hva_to_pfn_slow.
> >
> > hva_to_pfn_fast currently just fails for read-only faults. However,
> > there doesn't seem to be a reason that we can't just try pinning the
> > page without FOLL_WRITE instead of immediately falling back to slow-GUP.
> > This commit implements that behavior.
State what the patch does, avoid pronouns, and especially don't have "This commmit"
or "This patch" anywhere. From Documentation/process/submitting-patches.rst:
Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
to do frotz", as if you are giving orders to the codebase to change
its behaviour.
> > Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>
> > Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx>
> > ---
> > virt/kvm/kvm_main.c | 22 ++++++++++++----------
> > 1 file changed, 12 insertions(+), 10 deletions(-)
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index d255964ec331e..dae5f48151032 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2479,7 +2479,7 @@ static inline int check_user_page_hwpoison(unsigned long addr)
> > }
> >
> > /*
> > - * The fast path to get the writable pfn which will be stored in @pfn,
> > + * The fast path to get the pfn which will be stored in @pfn,
> > * true indicates success, otherwise false is returned. It's also the
> > * only part that runs if we can in atomic context.
> > */
> > @@ -2487,16 +2487,18 @@ static bool hva_to_pfn_fast(unsigned long addr, bool write_fault,
> > bool *writable, kvm_pfn_t *pfn)
> > {
> > struct page *page[1];
> > + bool found_by_fast_gup =
> > + get_user_page_fast_only(
> > + addr,
> > + /*
> > + * Fast pin a writable pfn only if it is a write fault request
> > + * or the caller allows to map a writable pfn for a read fault
> > + * request.
> > + */
> > + (write_fault || writable) ? FOLL_WRITE : 0,
> > + page);
> >
> > - /*
> > - * Fast pin a writable pfn only if it is a write fault request
> > - * or the caller allows to map a writable pfn for a read fault
> > - * request.
> > - */
> > - if (!(write_fault || writable))
> > - return false;
> > -
> > - if (get_user_page_fast_only(addr, FOLL_WRITE, page)) {
> > + if (found_by_fast_gup) {
>
> You could have a smaller diff (and arrive at something more readable)
Heh, this whole series just screams "google3". :-)
Anish, please read through
Documentation/process/coding-style.rst
and
Documentation/process/submitting-patches.rst
particularaly the "Describe your changes" and "Style-check your changes" your
changes sections. Bonus points if you work through the mostly redundant process/
documentation, e.g. these have supplementary info.
Documentation/process/4.Coding.rst
Documentation/process/5.Posting.rst
