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95920c2ed0
Helge reported that the introduction of PP_MAGIC_MASK let to crashes on
boot on his 32-bit parisc machine. The cause of this is the mask is set
too wide, so the page_pool_page_is_pp() incurs false positives which
crashes the machine.
Just disabling the check in page_pool_is_pp() will lead to the page_pool
code itself malfunctioning; so instead of doing this, this patch changes
the define for PP_DMA_INDEX_BITS to avoid mistaking arbitrary kernel
pointers for page_pool-tagged pages.
The fix relies on the kernel pointers that alias with the pp_magic field
always being above PAGE_OFFSET. With this assumption, we can use the
lowest bit of the value of PAGE_OFFSET as the upper bound of the
PP_DMA_INDEX_MASK, which should avoid the false positives.
Because we cannot rely on PAGE_OFFSET always being a compile-time
constant, nor on it always being >0, we fall back to disabling the
dma_index storage when there are not enough bits available. This leaves
us in the situation we were in before the patch in the Fixes tag, but
only on a subset of architecture configurations. This seems to be the
best we can do until the transition to page types in complete for
page_pool pages.
v2:
- Make sure there's at least 8 bits available and that the PAGE_OFFSET
bit calculation doesn't wrap
Link: https://lore.kernel.org/all/aMNJMFa5fDalFmtn@p100/
Fixes:
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History
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| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| cxl | ||
| drm | ||
| dt-bindings | ||
| hyperv | ||
| keys | ||
| kunit | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| rv | ||
| scsi | ||
| soc | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| ufs | ||
| vdso | ||
| video | ||
| xen | ||
| Kbuild | ||