On Thu, Mar 16, 2023 at 5:12 AM Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> wrote: > > On martedì 14 marzo 2023 04:56:08 CET Jason Wang wrote: > > On Thu, Mar 2, 2023 at 7:34 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> > wrote: > > > kmap_atomic() is deprecated in favor of kmap_local_page(). > > > > It's better to mention the commit or code that introduces this. > > > > > With kmap_local_page() the mappings are per thread, CPU local, can take > > > page-faults, and can be called from any context (including interrupts). > > > Furthermore, the tasks can be preempted and, when they are scheduled to > > > run again, the kernel virtual addresses are restored and still valid. > > > > > > kmap_atomic() is implemented like a kmap_local_page() which also disables > > > page-faults and preemption (the latter only for !PREEMPT_RT kernels, > > > otherwise it only disables migration). > > > > > > The code within the mappings/un-mappings in getu16_iotlb() and > > > putu16_iotlb() don't depend on the above-mentioned side effects of > > > kmap_atomic(), > > > > Note we used to use spinlock to protect simulators (at least until > > patch 7, so we probably need to re-order the patches at least) so I > > think this is only valid when: > > > > The vringh IOTLB helpers are not used in atomic context (e.g spinlock, > > interrupts). > > I'm probably missing some context but it looks that you are saying that > kmap_local_page() is not suited for any use in atomic context (you are > mentioning spinlocks). > > The commit message (that I know pretty well since it's the exact copy, word by > word, of my boiler plate commits) explains that kmap_local_page() is perfectly > usable in atomic context (including interrupts). Thanks for the confirmation, I misread the change log and thought it said it can't be used in interrupts. > > I don't know this code, however I am not able to see why these vringh IOTLB > helpers cannot work if used under spinlocks. Can you please elaborate a little > more? My fault, see above. > > > If yes, should we document this? (Or should we introduce a boolean to > > say whether an IOTLB variant can be used in an atomic context)? > > Again, you'll have no problems from the use of kmap_local_page() and so you > don't need any boolean to tell whether or not the code is running in atomic > context. > > Please take a look at the Highmem documentation which has been recently > reworked and extended by me: https://docs.kernel.org/mm/highmem.html This is really helpful. > > Anyway, I have been ATK 12 or 13 hours in a row. So I'm probably missing the > whole picture. It's me that misses the movitiation of kmap_local(). Thanks > > Thanks, > > Fabio > > > Thanks > > > > > so that mere replacements of the old API with the new one > > > is all that is required (i.e., there is no need to explicitly add calls > > > to pagefault_disable() and/or preempt_disable()). > > > > > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx> > > > --- > > > > > > Notes: > > > v2: > > > - added this patch since checkpatch.pl complained about deprecation > > > > > > of kmap_atomic() touched by next patch > > > > > > drivers/vhost/vringh.c | 8 ++++---- > > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c > > > index a1e27da54481..0ba3ef809e48 100644 > > > --- a/drivers/vhost/vringh.c > > > +++ b/drivers/vhost/vringh.c > > > @@ -1220,10 +1220,10 @@ static inline int getu16_iotlb(const struct vringh > > > *vrh,> > > > if (ret < 0) > > > > > > return ret; > > > > > > - kaddr = kmap_atomic(iov.bv_page); > > > + kaddr = kmap_local_page(iov.bv_page); > > > > > > from = kaddr + iov.bv_offset; > > > *val = vringh16_to_cpu(vrh, READ_ONCE(*(__virtio16 *)from)); > > > > > > - kunmap_atomic(kaddr); > > > + kunmap_local(kaddr); > > > > > > return 0; > > > > > > } > > > > > > @@ -1241,10 +1241,10 @@ static inline int putu16_iotlb(const struct vringh > > > *vrh,> > > > if (ret < 0) > > > > > > return ret; > > > > > > - kaddr = kmap_atomic(iov.bv_page); > > > + kaddr = kmap_local_page(iov.bv_page); > > > > > > to = kaddr + iov.bv_offset; > > > WRITE_ONCE(*(__virtio16 *)to, cpu_to_vringh16(vrh, val)); > > > > > > - kunmap_atomic(kaddr); > > > + kunmap_local(kaddr); > > > > > > return 0; > > > > > > } > > > > > > -- > > > 2.39.2 > > > >
