Re: [PATCH] efi/arm: fix allocation failure when reserving the kernel base

Chester Lin
2019-08-20T10:35:03Z

On Tue, Aug 20, 2019 at 10:49:30AM +0300, Mike Rapoport wrote:
> On Mon, Aug 19, 2019 at 05:56:51PM +0300, Ard Biesheuvel wrote:
> > On Mon, 19 Aug 2019 at 11:01, Chester Lin <clin@suse.com> wrote:
> > >
> > > Hi Mike and Ard,
> > >
> > > On Thu, Aug 15, 2019 at 04:37:39PM +0300, Mike Rapoport wrote:
> > > > On Thu, Aug 15, 2019 at 02:32:50PM +0300, Ard Biesheuvel wrote:
> > > > > (adding Mike)
> > > > >
>
> ...
>
> > > > > > In this case the kernel failed to reserve cma, which should hit the issue of
> > > > > > memblock_limit=0x1000 as I had mentioned in my patch description. The first
> > > > > > block [0-0xfff] was scanned in adjust_lowmem_bounds(), but it did not align
> > > > > > with PMD_SIZE so the cma reservation failed because the memblock.current_limit
> > > > > > was extremely low. That's why I expand the first reservation from 1 PAGESIZE to
> > > > > > 1 PMD_SIZE in my patch in order to avoid this issue. Please kindly let me know
> > > > > > if any suggestion, thank you.
> > > >
> > > >
> > > > > This looks like it is a separate issue. The memblock/cma code should
> > > > > not choke on a reserved page of memory at 0x0.
> > > > >
> > > > > Perhaps Russell or Mike (cc'ed) have an idea how to address this?
> > > >
> > > > Presuming that the last memblock dump comes from the end of
> > > > arm_memblock_init() with the this memory map
> > > >
> > > > memory[0x0] [0x0000000000000000-0x0000000000000fff], 0x0000000000001000 bytes flags: 0x4
> > > > memory[0x1] [0x0000000000001000-0x0000000007ef5fff], 0x0000000007ef5000 bytes flags: 0x0
> > > > memory[0x2] [0x0000000007ef6000-0x0000000007f09fff], 0x0000000000014000 bytes flags: 0x4
> > > > memory[0x3] [0x0000000007f0a000-0x000000003cb3efff], 0x0000000034c35000 bytes flags: 0x0
> > > >
> > > > adjust_lowmem_bounds() will set the memblock_limit (and respectively global
> > > > memblock.current_limit) to 0x1000 and any further memblock_alloc*() will
> > > > happily fail.
> > > >
> > > > I believe that the assumption for memblock_limit calculations was that the
> > > > first bank has several megs at least.
> > > >
> > > > I wonder if this hack would help:
> > > >
> > > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > > > index d9a0038..948e5b9 100644
> > > > --- a/arch/arm/mm/mmu.c
> > > > +++ b/arch/arm/mm/mmu.c
> > > > @@ -1206,7 +1206,7 @@ void __init adjust_lowmem_bounds(void)
> > > > * allocated when mapping the start of bank 0, which
> > > > * occurs before any free memory is mapped.
> > > > */
> > > > - if (!memblock_limit) {
> > > > + if (memblock_limit < PMD_SIZE) {
> > > > if (!IS_ALIGNED(block_start, PMD_SIZE))
> > > > memblock_limit = block_start;
> > > > else if (!IS_ALIGNED(block_end, PMD_SIZE))
> > > >
> > >
> > > I applied this patch as well and it works well on rpi-2 model B.
> > >
> >
> > Thanks, Chester, that is good to know.
> >
> > However, afaict, this only affects systems where physical memory
> > starts at address 0x0, so I think we need a better fix.
>
> This hack can be easily extended to handle systems with arbitrary start
> address, but it's still a hack...
>
> > I know Mike has been looking into the NOMAP stuff lately, and your
> > original patch contains a hunk that makes this code (?) disregard
> > nomap memblocks. That might be a better approach.
>
> I was actually looking how to replace NOMAP with something else to make
> memblock.memory consistent with actual physical memory banks. But this work
> is stashed for now.
>
> I'm not sure that skipping NOMAP regions would be good enough.
> If I understand corrrectly, with Chester's original patch the reservation
> of PMD aligned chunk of 32M for the kernel made the first conv-mem region
> PMD aligned and then memblock_limit will be set to the end of this region.
>
> Is there a reason for marking EFI_RESERVED_TYPE as NOMAP rather than simply
> reserve them with memblock_reserve()?
>

Hi Mike,

I make this change in efistub so I am not sure if memblock_reserve() can be
linked by ld or not. I tried using efi_mem_reserve() but got a linker error of
undefined reference. Is there a better place to call memblock_reserve() after
efistub?

Thanks,
Chester