4.20-stable review patch. If anyone has any objections, please let me know.
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From: Michael Ellerman mpe@ellerman.id.au
commit a58007621be33e9f7c7bed5d5ff8ecb914e1044a upstream.
In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT rather than just checking that the value is non-zero, e.g.:
static inline int pgd_present(pgd_t pgd) { - return !pgd_none(pgd); + return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); }
Unfortunately this is broken on big endian, as the result of the bitwise & is truncated to int, which is always zero because _PAGE_PRESENT is 0x8000000000000000ul. This means pgd_present() and pud_present() are always false at compile time, and the compiler elides the subsequent code.
Remarkably with that bug present we are still able to boot and run with few noticeable effects. However under some work loads we are able to trigger a warning in the ext4 code:
WARNING: CPU: 11 PID: 29593 at fs/ext4/inode.c:3927 .ext4_set_page_dirty+0x70/0xb0 CPU: 11 PID: 29593 Comm: debugedit Not tainted 4.20.0-rc1 #1 ... NIP .ext4_set_page_dirty+0x70/0xb0 LR .set_page_dirty+0xa0/0x150 Call Trace: .set_page_dirty+0xa0/0x150 .unmap_page_range+0xbf0/0xe10 .unmap_vmas+0x84/0x130 .unmap_region+0xe8/0x190 .__do_munmap+0x2f0/0x510 .__vm_munmap+0x80/0x110 .__se_sys_munmap+0x14/0x30 system_call+0x5c/0x70
The fix is simple, we need to convert the result of the bitwise & to an int before returning it.
Thanks to Erhard, Jan Kara and Aneesh for help with debugging.
Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit") Cc: stable@vger.kernel.org # v4.20+ Reported-by: Erhard F. erhard_f@mailbox.org Reviewed-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/include/asm/book3s/64/pgtable.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h @@ -904,7 +904,7 @@ static inline int pud_none(pud_t pud)
static inline int pud_present(pud_t pud) { - return (pud_raw(pud) & cpu_to_be64(_PAGE_PRESENT)); + return !!(pud_raw(pud) & cpu_to_be64(_PAGE_PRESENT)); }
extern struct page *pud_page(pud_t pud); @@ -951,7 +951,7 @@ static inline int pgd_none(pgd_t pgd)
static inline int pgd_present(pgd_t pgd) { - return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); + return !!(pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT)); }
static inline pte_t pgd_pte(pgd_t pgd)