74 lines
3.4 KiB
Diff
74 lines
3.4 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Fri, 29 Jul 2022 15:57:57 -0400
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Subject: [PATCH] efi: make the default arena most of ram
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Currently when populating the initial memory arena on EFI systems, we
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count the available regions below GRUB_EFI_MAX_ALLOCATION_ADDRESS from
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the EFI memory map and then allocates one quarter of that for our arena.
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Because many systems come up without IOMMUs, we currently set
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GRUB_EFI_MAX_ALLOCATION_ADDRESS to 0x7fffffff, i.e. all addresses
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allocated must be below 2G[0]. Due to firmware and other
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considerations, this makes the most memory we can possibly have in our
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arena 512M.
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Because our EFI loader doesn't get kernel and initrd memory from grub's
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allocator, but rather reserves it directly from UEFI and then simply
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marks those as allocated if they're within grub's arena, it was
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historically possible to have initrds that are larger than 512M, because
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we could use any memory region below 4G, without concern for grub's
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choice of arena size.
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Unfortunately, when we switched to using the "verifiers" API (and thus
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the file_filter_t API) to do measurement of kernel and initrd, this
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introduced a pattern that allocates the entire file when we call
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grub_file_open(), and buffers it to pass to the filter. This results in
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needing to have enough space for the initramfs in the grub arena.
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This is bad.
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Since it's unlikely you're going to do anything *other* than loading a
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kernel and initramfs that takes much of the available free memory from
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UEFI, this patch introduces a workaround by changing the amount we give
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to the arena be three quarters of the available memory, rather than one
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quarter, thus changing our theoretical initrd limit to 1.5G. In
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practice, it may still be smaller than that depending on allocation
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fragmentation, but generally it will be most of it.
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Note that this doesn't fix the underlying flaw, which is that there is
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no safe way to do the validation correctly using the "verifiers" system
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with the current file API without buffering the whole file before
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grub_file_read() is ever called, and thus you can't set an allocation
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policy for the initial buffer of the file at all, so unless we raise the
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allocation limit to >4G, it can't be allocated in the big region.
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[0] I'm not sure there was a good reason not to pick 4G, but even if we
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had, at least one common firmware routes the first 2G of physical
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RAM to 0x0, and any additional memory starting at 0x100000000.
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Related: rhbz#2112134
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Signed-off-by: Peter Jones <pjones@redhat.com>
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---
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grub-core/kern/efi/mm.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/grub-core/kern/efi/mm.c b/grub-core/kern/efi/mm.c
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index e460b072e6..150e412ee7 100644
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--- a/grub-core/kern/efi/mm.c
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+++ b/grub-core/kern/efi/mm.c
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@@ -737,10 +737,10 @@ grub_efi_mm_init (void)
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filtered_memory_map_end = filter_memory_map (memory_map, filtered_memory_map,
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desc_size, memory_map_end);
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- /* By default, request a quarter of the available memory. */
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+ /* By default, request three quarters of the available memory. */
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total_pages = get_total_pages (filtered_memory_map, desc_size,
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filtered_memory_map_end);
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- required_pages = (total_pages >> 2);
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+ required_pages = (total_pages >> 1) + (total_pages >> 2);
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if (required_pages < BYTES_TO_PAGES (MIN_HEAP_SIZE))
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required_pages = BYTES_TO_PAGES (MIN_HEAP_SIZE);
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else if (required_pages > BYTES_TO_PAGES (MAX_HEAP_SIZE))
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