| Message ID | 20200811182457.57957-1-jrtc27@jrtc27.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] arch/ia64: Restore arch-specific pgd_offset_k implementation | expand |
On Tue, Aug 11, 2020 at 07:24:57PM +0100, Jessica Clarke wrote: > IA-64 is special and treats pgd_offset_k differently from pgd_offset by > not including the region number, and init_mm's PGD is such that it only > points to the kernel's region's PGD. This was broken in 974b9b2c68 which > unified the two and therefore included the region number, causing it to > go way out of bounds of the kernel's PGD, which made the kernel hang > during early boot. Thus, permit pgd_offset_k to be overridden like the > other macros and override it on IA-64 with the old implementation. Also > update the comment to clarify that this is not just an optimisation but > a required implementation detail. If I may suggest: IA-64 is special and treats pgd_offset_k() differently from pgd_offset() by using different formulas to calculate index into kernel and user PGD tables. The index into user PGDs takes into account the region number and the index into the kernel (init_mm) PGD always presumes predefined kernel region number. Commit 974b9b2c68 ("mm: consolidate pte_index() and pte_offset_*() definitions") made IA-64 to use generic pgd_offset_k() which wrongly used pgd_index() for user page tables. As the result, the index into kernel PGD was going out of bounds and the kernel hang during early boot. Allow overrides of pgd_offset_k() and use an override on IA-64 with the old implementation that will correctly index kernel PGD. > Fixes: 974b9b2c68 ("mm: consolidate pte_index() and pte_offset_*() definitions") > Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> > Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com> > Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> Thanks for the fix, I don't insist on the changelog update, so with the nit below Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> > --- > Changes since v1: > * Fixed typo in commit message > * Slightly reworded commit message to sound less weird > * Included Adrian's Tested-by > > arch/ia64/include/asm/pgtable.h | 8 ++++++++ > include/linux/pgtable.h | 2 ++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/ia64/include/asm/pgtable.h b/arch/ia64/include/asm/pgtable.h > index 10850897a91c..2ac2199d99ce 100644 > --- a/arch/ia64/include/asm/pgtable.h > +++ b/arch/ia64/include/asm/pgtable.h > @@ -366,6 +366,14 @@ pgd_index (unsigned long address) > } > #define pgd_index pgd_index > > +/* > + * In the kernel's mapped region we know everything is in region number 5, so > + * as an optimisation its PGD already points to the area for that region, but > + * that means not adding the region here is required, not just an optimisation. > + */ How about: /* * In the kernel's mapped region we know everything is in region number 5, so * as an optimisation its PGD already points to the area for that region. * However, this also means that we cannot use pgd_index() and we never * should add the region here. */ > +#define pgd_offset_k(addr) \ > + (init_mm.pgd + (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))) > + > /* Look up a pgd entry in the gate area. On IA-64, the gate-area > resides in the kernel-mapped segment, hence we use pgd_offset_k() > here. */ > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 53e97da1e8e2..73c64fe098ba 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -117,7 +117,9 @@ static inline pgd_t *pgd_offset_pgd(pgd_t *pgd, unsigned long address) > * a shortcut which implies the use of the kernel's pgd, instead > * of a process's > */ > +#ifndef pgd_offset_k > #define pgd_offset_k(address) pgd_offset(&init_mm, (address)) > +#endif > > /* > * In many cases it is known that a virtual address is mapped at PMD or PTE > -- > 2.23.0 >
diff --git a/arch/ia64/include/asm/pgtable.h b/arch/ia64/include/asm/pgtable.h index 10850897a91c..2ac2199d99ce 100644 --- a/arch/ia64/include/asm/pgtable.h +++ b/arch/ia64/include/asm/pgtable.h @@ -366,6 +366,14 @@ pgd_index (unsigned long address) } #define pgd_index pgd_index +/* + * In the kernel's mapped region we know everything is in region number 5, so + * as an optimisation its PGD already points to the area for that region, but + * that means not adding the region here is required, not just an optimisation. + */ +#define pgd_offset_k(addr) \ + (init_mm.pgd + (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))) + /* Look up a pgd entry in the gate area. On IA-64, the gate-area resides in the kernel-mapped segment, hence we use pgd_offset_k() here. */ diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 53e97da1e8e2..73c64fe098ba 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -117,7 +117,9 @@ static inline pgd_t *pgd_offset_pgd(pgd_t *pgd, unsigned long address) * a shortcut which implies the use of the kernel's pgd, instead * of a process's */ +#ifndef pgd_offset_k #define pgd_offset_k(address) pgd_offset(&init_mm, (address)) +#endif /* * In many cases it is known that a virtual address is mapped at PMD or PTE
IA-64 is special and treats pgd_offset_k differently from pgd_offset by not including the region number, and init_mm's PGD is such that it only points to the kernel's region's PGD. This was broken in 974b9b2c68 which unified the two and therefore included the region number, causing it to go way out of bounds of the kernel's PGD, which made the kernel hang during early boot. Thus, permit pgd_offset_k to be overridden like the other macros and override it on IA-64 with the old implementation. Also update the comment to clarify that this is not just an optimisation but a required implementation detail. Fixes: 974b9b2c68 ("mm: consolidate pte_index() and pte_offset_*() definitions") Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com> Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> --- Changes since v1: * Fixed typo in commit message * Slightly reworded commit message to sound less weird * Included Adrian's Tested-by arch/ia64/include/asm/pgtable.h | 8 ++++++++ include/linux/pgtable.h | 2 ++ 2 files changed, 10 insertions(+)