On Thu, Dec 01, 2022 at 04:11:58PM -0500, Stefan Berger wrote:
> From: Daniel Axtens <d...@axtens.net>
>
> On powerpc-ieee1275, we are running out of memory trying to verify
> anything. This is because:
>
> - we have to load an entire file into memory to verify it. This is
> difficult to change with appended signatures.
> - We only have 32MB of heap.
> - Distro kernels are now often around 30MB.
>
> So we want to be able to claim more memory from OpenFirmware for our heap
> at runtime.
>
> There are some complications:
>
> - The grub mm code isn't the only thing that will make claims on
> memory from OpenFirmware:
>
> * PFW/SLOF will have claimed some for their own use.
>
> * The ieee1275 loader will try to find other bits of memory that we
> haven't claimed to place the kernel and initrd when we go to boot.
>
> * Once we load Linux, it will also try to claim memory. It claims
> memory without any reference to /memory/available, it just starts
> at min(top of RMO, 768MB) and works down. So we need to avoid this
> area. See arch/powerpc/kernel/prom_init.c as of v5.11.
>
> - The smallest amount of memory a ppc64 KVM guest can have is 256MB.
> It doesn't work with distro kernels but can work with custom kernels.
> We should maintain support for that. (ppc32 can boot with even less,
> and we shouldn't break that either.)
>
> - Even if a VM has more memory, the memory OpenFirmware makes available
> as Real Memory Area can be restricted. Even with our CAS work, an LPAR
> on a PowerVM box is likely to have only 512MB available to OpenFirmware
> even if it has many gigabytes of memory allocated.
>
> What should we do?
>
> We don't know in advance how big the kernel and initrd are going to be,
> which makes figuring out how much memory we can take a bit tricky.
>
> To figure out how much memory we should leave unused, I looked at:
>
> - an Ubuntu 20.04.1 ppc64le pseries KVM guest:
> vmlinux: ~30MB
> initrd: ~50MB
>
> - a RHEL8.2 ppc64le pseries KVM guest:
> vmlinux: ~30MB
> initrd: ~30MB
>
> So to give us a little wriggle room, I think we want to leave at least
> 128MB for the loader to put vmlinux and initrd in memory and leave Linux
> with space to satisfy its early allocations.
>
> Allow other space to be allocated at runtime.
>
> Tested-by: Stefan Berger <stef...@linux.ibm.com>
> Signed-off-by: Daniel Axtens <d...@axtens.net>
[...]
> +static grub_err_t grub_ieee1275_mm_add_region (grub_size_t size, unsigned
> int flags)
static grub_err_t
grub_ieee1275_mm_add_region (grub_size_t size, unsigned int flags)
> +{
> + grub_uint32_t total = size;
> + grub_uint32_t free_memory = 0;
> +
> + grub_dprintf ("ieee1275", "mm requested region of size %x, flags %x\n",
> + size, flags);
> +
> + /*
> + * Update free memory each time, which is a bit inefficient but guards us
> + * against a situation where some OF driver goes out to firmware for
> + * memory and we don't realise.
> + */
> + grub_machine_mmap_iterate (count_free, &free_memory);
> +
> + /* Ensure we leave enough space to boot. */
> + if (free_memory <= RUNTIME_MIN_SPACE + size)
> + {
> + grub_dprintf ("ieee1275", "Cannot satisfy allocation and retain
> minimum runtime space\n");
> + return GRUB_ERR_OUT_OF_MEMORY;
> + }
> +
> + grub_dprintf ("ieee1275", "free = 0x%x\n", free_memory);
> +
> + if (flags & GRUB_MM_ADD_REGION_CONSECUTIVE)
> + {
> + /* first try rounding up hard for the sake of speed */
> + total = grub_max (ALIGN_UP(size, 1024 * 1024) + 1024 * 1024, 32 * 1024
> * 1024);
s/ALIGN_UP(/ALIGN_UP (/
> + total = grub_min (free_memory - RUNTIME_MIN_SPACE, total);
> +
> + grub_dprintf ("ieee1275", "looking for %x bytes of memory (%x
> requested)\n", total, size);
> +
> + grub_machine_mmap_iterate (region_claim, &total);
> + grub_dprintf ("ieee1275", "get memory from fw %s\n", total == 0 ?
> "succeeded" : "failed");
> +
> + /* fallback: requested size + padding for a grub_mm_header_t and
> region */
This...
> + if (total != 0)
> + {
> + total = size + 48;
... and this should be dropped. I think this patch set, [1], [2], solves
this kinds of problems in general. Please take a look...
> + total = grub_min (free_memory - RUNTIME_MIN_SPACE, total);
> +
> + grub_dprintf ("ieee1275", "fallback for %x bytes of memory (%x
> requested)\n", total, size);
> +
> + grub_machine_mmap_iterate (region_claim, &total);
> + grub_dprintf ("ieee1275", "fallback from fw %s\n", total == 0 ?
> "succeeded" : "failed");
> + }
> + }
> + else
> + {
> + /* provide padding for a grub_mm_header_t and region */
> + total = size + 48;
Ditto... And then probably total can be dropped too...
> + total = grub_min (free_memory - RUNTIME_MIN_SPACE, total);
> + grub_machine_mmap_iterate (heap_init, &total);
> + grub_dprintf ("ieee1275", "get noncontig memory from fw %s\n", total
> == 0 ? "succeeded" : "failed");
> + }
> +
> + if (total == 0)
> + return GRUB_ERR_NONE;
> + else
> + return GRUB_ERR_OUT_OF_MEMORY;
> +}
Daniel
[1] https://lists.gnu.org/archive/html/grub-devel/2022-11/msg00147.html
[2] https://lists.gnu.org/archive/html/grub-devel/2022-12/msg00115.html
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