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authorAndy Lutomirski <luto@kernel.org>2016-07-22 21:58:08 -0700
committerIngo Molnar <mingo@kernel.org>2016-07-23 21:13:25 +0200
commit530dd8d4b9daf77e3e5d145a26210d91ced954c7 (patch)
tree27d8ea050147c632ce7e54997cd61caa770851d1 /arch/x86/platform
parent3ebfd81f7fb3e81a754e37283b7f38c62244641a (diff)
x86/mm/cpa: Fix populate_pgd(): Stop trying to deallocate failed PUDs
Valdis Kletnieks bisected a boot failure back to this recent commit: 360cb4d15567 ("x86/mm/cpa: In populate_pgd(), don't set the PGD entry until it's populated") I broke the case where a PUD table got allocated -- populate_pud() would wander off a pgd_none entry and get lost. I'm not sure how this survived my testing. Fix the original issue in a much simpler way. The problem was that, if we allocated a PUD table, failed to populate it, and freed it, another CPU could potentially keep using the PGD entry we installed (either by copying it via vmalloc_fault or by speculatively caching it). There's a straightforward fix: simply leave the top-level entry in place if this happens. This can't waste any significant amount of memory -- there are at most 256 entries like this systemwide and, as a practical matter, if we hit this failure path repeatedly, we're likely to reuse the same page anyway. For context, this is a reversion with this hunk added in: if (ret < 0) { + /* + * Leave the PUD page in place in case some other CPU or thread + * already found it, but remove any useless entries we just + * added to it. + */ - unmap_pgd_range(cpa->pgd, addr, + unmap_pud_range(pgd_entry, addr, addr + (cpa->numpages << PAGE_SHIFT)); return ret; } This effectively open-codes what the now-deleted unmap_pgd_range() function used to do except that unmap_pgd_range() used to try to free the page as well. Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Luis R. Rodriguez <mcgrof@suse.com> Cc: Mike Krinkin <krinkin.m.u@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Toshi Kani <toshi.kani@hp.com> Link: http://lkml.kernel.org/r/21cbc2822aa18aa812c0215f4231dbf5f65afa7f.1469249789.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/platform')
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