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authorClaudio Imbrenda <imbrenda@linux.ibm.com>2020-04-01 21:05:56 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-02 09:35:27 -0700
commitf28d43636d6f940e60abef4f0131119836c8ebd4 (patch)
treebcfe67977bfdc80f83fc05ad4b7ac8d834741015 /mm/page-writeback.c
parentdc8fb2f282ad13e550b65958fea40c7eb766d42a (diff)
downloadlinux-f28d43636d6f940e60abef4f0131119836c8ebd4.tar.bz2
mm/gup/writeback: add callbacks for inaccessible pages
With the introduction of protected KVM guests on s390 there is now a concept of inaccessible pages. These pages need to be made accessible before the host can access them. While cpu accesses will trigger a fault that can be resolved, I/O accesses will just fail. We need to add a callback into architecture code for places that will do I/O, namely when writeback is started or when a page reference is taken. This is not only to enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory. We do not want userspace to be able to trigger I/O errors and thus the logic is "whenever somebody accesses that page (gup) or does I/O, make sure that this page can be accessed". When the guest tries to access that page we will wait in the page fault handler for writeback to have finished and for the page_ref to be the expected value. On s390x the function is not supposed to fail, so it is ok to use a WARN_ON on failure. If we ever need some more finegrained handling we can tackle this when we know the details. Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Acked-by: Will Deacon <will@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Matthew Wilcox <willy@infradead.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Link: http://lkml.kernel.org/r/20200306132537.783769-3-imbrenda@linux.ibm.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page-writeback.c')
-rw-r--r--mm/page-writeback.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d9c42d38ee47..7326b54ab728 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2764,7 +2764,7 @@ int test_clear_page_writeback(struct page *page)
int __test_set_page_writeback(struct page *page, bool keep_write)
{
struct address_space *mapping = page_mapping(page);
- int ret;
+ int ret, access_ret;
lock_page_memcg(page);
if (mapping && mapping_use_writeback_tags(mapping)) {
@@ -2807,6 +2807,13 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
}
unlock_page_memcg(page);
+ access_ret = arch_make_page_accessible(page);
+ /*
+ * If writeback has been triggered on a page that cannot be made
+ * accessible, it is too late to recover here.
+ */
+ VM_BUG_ON_PAGE(access_ret != 0, page);
+
return ret;
}