Messages in this thread | | | Date | Wed, 27 Jan 2016 15:31:37 +0100 | Subject | Re: [PATCH v3 07/21] arm64: move kernel image to base of vmalloc area | From | Ard Biesheuvel <> |
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On 15 January 2016 at 12:23, Mark Rutland <mark.rutland@arm.com> wrote: > On Fri, Jan 15, 2016 at 10:54:26AM +0100, Ard Biesheuvel wrote: >> On 14 January 2016 at 19:57, Mark Rutland <mark.rutland@arm.com> wrote: >> > On Wed, Jan 13, 2016 at 01:51:10PM +0000, Mark Rutland wrote: >> >> On Wed, Jan 13, 2016 at 09:39:41AM +0100, Ard Biesheuvel wrote: >> >> > If I remove the rounding, I get false positive kasan errors which I >> >> > have not quite diagnosed yet, but are probably due to the fact that >> >> > the rounding performed by vmemmap_populate() goes in the wrong >> >> > direction. >> > >> > As far as I can see, it implicitly rounds the base down and end up to >> > SWAPPER_BLOCK_SIZE granularity. >> > >> > I can see that it might map too much memory, but I can't see why that >> > should trigger KASAN failures. Regardless of what was mapped KASAN >> > should stick to the region it cares about, and everything else should >> > stay out of that. >> > >> > When do you see the failures, and are they in any way consistent? >> > >> > Do you have an example to hand? >> > >> >> For some reason, this issue has evaporated, i.e., I can no longer >> reproduce it on my WIP v4 branch. >> So I will remove the rounding. > > Ok. > > I'll let you know if I stumble across anything that looks like a > potential cause of the KASAN failures, and I'll try to give v4 a go at > some point soon. >
OK, I managed to track this down (I think). The issue here is that, while vmemmap_populate() does the right thing wrt the start and end boundaries, populate_zero_shadow() will map the adjoining regions down to page granularity, replacing vmemmap_populate()'s PMD block mappings with PMD table mappings. So I need to put back the rounding (I removed it in v4)
Thanks, Ard.
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