Messages in this thread | | | Subject | Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory | From | Dave Hansen <> | Date | Thu, 12 Aug 2021 14:43:19 -0700 |
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On 8/12/21 2:14 PM, Kirill A. Shutemov wrote: > On Tue, Aug 10, 2021 at 10:50:33AM -0700, Dave Hansen wrote: >>> + if ((start & PMD_MASK) == (end & PMD_MASK)) { >>> + npages = (end - start) / PAGE_SIZE; >>> + __accept_memory(start, start + npages * PAGE_SIZE); >>> + return; >>> + } >> >> Hmm, is it possible to have this case hit, but neither of the two below >> cases? This seems to be looking for a case where the range is somehow >> entirely contained in one PMD_SIZE area, but where it doesn't consume a >> whole area. >> >> Wouldn't that mean that 'start' or 'end' must be unaligned? > > The problem is that if both of them unaligned round_up() and round_down() > in the cases below would step outside the requested range.
Ahh, got it.
You might want to add some comments like:
/* Immediately accept whole thing if within a PMD_SIZE block: */
/* Immediately accept a <PMD_SIZE piece at the start: */
/* Immediately accept a <PMD_SIZE piece at the end: */
/* Mark full PMD_SIZE areas so they can be accepted later */
To the three if statements and the bitmap_set().
After looking at this, I do think you probably did this the simplest way possible. It just needs a little help.
>>> + if (start & ~PMD_MASK) { >>> + npages = (round_up(start, PMD_SIZE) - start) / PAGE_SIZE; >>> + __accept_memory(start, start + npages * PAGE_SIZE); >>> + start = round_up(start, PMD_SIZE); >>> + } >>> + >>> + if (end & ~PMD_MASK) { >>> + npages = (end - round_down(end, PMD_SIZE)) / PAGE_SIZE; >>> + end = round_down(end, PMD_SIZE); >>> + __accept_memory(end, end + npages * PAGE_SIZE); >>> + } >>> + npages = (end - start) / PMD_SIZE; >>> + bitmap_set((unsigned long *)params->unaccepted_memory, >>> + start / PMD_SIZE, npages); >>> +}
One note as I'm looking at this again: 'npages' can be 0. Imagine if you had an 8k region that started with the last 4k page of a 2M area and ended on the first 4k page of the next 2M area, like 0x1ff000->0x201000.
I think it's harmless and bitmap_set() seems to handle it correctly. But, it's probably worth a comment because it's not obvious.
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