On 08/03/22 at 06:00pm, Fabio M. De Francesco wrote: Thanks for the log update. And Cc Andrew.
> kmap() is being deprecated in favor of kmap_local_page(). > > There are two main problems with kmap(): (1) It comes with an overhead as > mapping space is restricted and protected by a global lock for > synchronization and (2) it also requires global TLB invalidation when the > kmap’s pool wraps and it might block when the mapping space is fully > utilized until a slot becomes available. > > With kmap_local_page() the mappings are per thread, CPU local, can take > page faults, and can be called from any context (including interrupts). > It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, > the tasks can be preempted and, when they are scheduled to run again, the > kernel virtual addresses are restored and are still valid. > > Since its use in kexec_core.c is safe everywhere, it should be preferred. > > Therefore, replace kmap() with kmap_local_page() in kexec_core.c. > > Tested on a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with > HIGHMEM64GB enabled. > > Suggested-by: Ira Weiny <[email protected]> > Reviewed-by: Ira Weiny <[email protected]> > Acked-by: Baoquan He <[email protected]> > Signed-off-by: Fabio M. De Francesco <[email protected]> > --- > > v2->v3: Add more information in the commit message as requested by Baoquan > He and forward two tags, respectively from Ira Weiny and Baoquan He (many > thanks to them two!). > > v1->v2: A sentence of the commit message contained an error due to a > mistake in copy-pasting from a previous patch. Replace "aio.c" with > "kexec_core.c". > > kernel/kexec_core.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index 4d34c78334ce..6f98274765d4 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -814,7 +814,7 @@ static int kimage_load_normal_segment(struct kimage > *image, > if (result < 0) > goto out; > > - ptr = kmap(page); > + ptr = kmap_local_page(page); > /* Start with a clear page */ > clear_page(ptr); > ptr += maddr & ~PAGE_MASK; > @@ -827,7 +827,7 @@ static int kimage_load_normal_segment(struct kimage > *image, > memcpy(ptr, kbuf, uchunk); > else > result = copy_from_user(ptr, buf, uchunk); > - kunmap(page); > + kunmap_local(ptr); > if (result) { > result = -EFAULT; > goto out; > @@ -878,7 +878,7 @@ static int kimage_load_crash_segment(struct kimage *image, > goto out; > } > arch_kexec_post_alloc_pages(page_address(page), 1, 0); > - ptr = kmap(page); > + ptr = kmap_local_page(page); > ptr += maddr & ~PAGE_MASK; > mchunk = min_t(size_t, mbytes, > PAGE_SIZE - (maddr & ~PAGE_MASK)); > @@ -894,7 +894,7 @@ static int kimage_load_crash_segment(struct kimage *image, > else > result = copy_from_user(ptr, buf, uchunk); > kexec_flush_icache_page(page); > - kunmap(page); > + kunmap_local(ptr); > arch_kexec_pre_free_pages(page_address(page), 1); > if (result) { > result = -EFAULT; > -- > 2.37.1 > _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
