On Tue, 11 Jul 2017 08:44:15 -0700 Ram Pai <linuxram@xxxxxxxxxx> wrote: > On Tue, Jul 11, 2017 at 03:59:59PM +1000, Balbir Singh wrote: > > On Wed, 5 Jul 2017 14:21:39 -0700 > > Ram Pai <linuxram@xxxxxxxxxx> wrote: > > > > > Rearrange 64K PTE bits to free up bits 3, 4, 5 and 6 > > > in the 64K backed HPTE pages. This along with the earlier > > > patch will entirely free up the four bits from 64K PTE. > > > The bit numbers are big-endian as defined in the ISA3.0 > > > > > > This patch does the following change to 64K PTE backed > > > by 64K HPTE. > > > > > > H_PAGE_F_SECOND (S) which occupied bit 4 moves to the > > > second part of the pte to bit 60. > > > H_PAGE_F_GIX (G,I,X) which occupied bit 5, 6 and 7 also > > > moves to the second part of the pte to bit 61, > > > 62, 63, 64 respectively > > > > > > since bit 7 is now freed up, we move H_PAGE_BUSY (B) from > > > bit 9 to bit 7. > > > > > > The second part of the PTE will hold > > > (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63. > > > > > > Before the patch, the 64K HPTE backed 64k PTE format was > > > as follows > > > > > > 0 1 2 3 4 5 6 7 8 9 10...........................63 > > > : : : : : : : : : : : : > > > v v v v v v v v v v v v > > > > > > ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-, > > > |x|x|x| |S |G |I |X |x|B|x|x|x|................|.|.|.|.| <- primary pte > > > '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_' > > > | | | | | | | | | | | | |..................| | | | | <- secondary pte > > > '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_' > > > > > > > It's not entirely clear what the secondary pte contains > > today and how many of the bits are free today? > > The secondary pte today is not used for anything for 64k-hpte > backed ptes. It gets used the moment the pte gets backed by > 4-k hptes. Till then the bits are available. And this patch > makes use of that knowledge. OK.. but does this mean subpage-protection? Or do you mean page size demotion? I presume it's the later. Balbir Singh.
