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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C4E0721108 X-Spam-Level: X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[15]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -4.51 X-Spam-Flag: NO On 12/4/24 18:33, Zi Yan wrote: > On 4 Dec 2024, at 11:29, Matthew Wilcox wrote: > >> On Wed, Dec 04, 2024 at 11:16:51AM -0500, Zi Yan wrote: >>>> So maybe the clearing done as part of page allocator isn't enough here. >>>> >>> Basically, mips needs to flush data cache if kmap address is aliased to >> >> People use "aliased" in contronym ways. Do you mean "has a >> non-congruent alias" or "has a congruent alias"? >> >>> userspace address. This means when mips has THP on, the patch below >>> is not enough to fix the issue. >>> >>> In post_alloc_hook(), it does not make sense to pass userspace address >>> in to determine whether to flush dcache or not. >>> >>> One way to fix it is to add something like arch_userpage_post_alloc() >>> to flush dcache if kmap address is aliased to userspace address. >>> But my questions are that >>> 1) if kmap address will always be the same for two separate kmap_local() calls, >> >> No. It just takes the next address in the stack. > > Hmm, if kmap_local() gives different addresses, wouldn’t init_on_alloc be > causing issues before my patch? In the page allocator, the page is zeroed > from one kmap address without flush, then clear_user_highpage() clears > it again with another kmap address with flush. After returning to userspace, > the user application works on the page but when the cache line used by > init_on_alloc is written back (with 0s) at eviction, user data is corrupted. > Am I missing anything? Or all arch with cache aliasing never enables > init_on_alloc? Maybe the arch also defines some hooks like arch_kmap_local_post_unmap() ? As for the fix, could it rely on e.g. __HAVE_ARCH_COPY_USER_HIGHPAGE instead of CONFIG_MIPS? That affects more arches, I don't know if we broke only mips or others too. > Best Regards, > Yan, Zi