Re: [PATCH 1/3] x86/setup: always reserve the first 1M of RAM
From: Mike Rapoport <rppt@kernel.org>
Date: 2021-06-01 17:19:27
Also in:
linux-efi, lkml, platform-driver-x86
Hi Baoquan, On Tue, Jun 01, 2021 at 05:06:53PM +0800, Baoquan He wrote:
On 06/01/21 at 10:53am, Mike Rapoport wrote:quoted
From: Mike Rapoport <redacted>......quoted
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c index 7850111008a8..b15ebfe40a73 100644 --- a/arch/x86/platform/efi/quirks.c +++ b/arch/x86/platform/efi/quirks.c@@ -450,6 +450,18 @@ void __init efi_free_boot_services(void) size -= rm_size; }Thanks for taking care of the low-1M excluding in efi_free_boot_services(), Mike. You might want to remove the old real mode excluding code either since it's been covered by your new code.
Unfortunately I can't because it's important that set_real_mode_mem() would
reuse memory that was occupied by EFI boot services and that is being freed
here.
According to the changelog of 5bc653b73182 ("x86/efi: Allocate a trampoline
if needed in efi_free_boot_services()"), that system has EBDA at 0x2c000 so
we reserve everything from 0x2c000 to 0xa0000 in reserve_bios_regions() and
most of the memory below 0x2c0000 is used by EFI boot data. So with such
memory layout reserve_real_mode() won't be able to allocate the trampoline.
Yet, when the EFI boot data is free, the room occupied by it will be reused
by the real mode trampoline via set_real_mode_mem().
quoted hunk ↗ jump to hunk
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c index b15ebfe40a73..be814f2089ff 100644 --- a/arch/x86/platform/efi/quirks.c +++ b/arch/x86/platform/efi/quirks.c@@ -409,7 +409,6 @@ void __init efi_free_boot_services(void) for_each_efi_memory_desc(md) { unsigned long long start = md->phys_addr; unsigned long long size = md->num_pages << EFI_PAGE_SHIFT; - size_t rm_size; if (md->type != EFI_BOOT_SERVICES_CODE && md->type != EFI_BOOT_SERVICES_DATA) {@@ -430,26 +429,6 @@ void __init efi_free_boot_services(void) */ efi_unmap_pages(md); - /* - * Nasty quirk: if all sub-1MB memory is used for boot - * services, we can get here without having allocated the - * real mode trampoline. It's too late to hand boot services - * memory back to the memblock allocator, so instead - * try to manually allocate the trampoline if needed. - * - * I've seen this on a Dell XPS 13 9350 with firmware - * 1.4.4 with SGX enabled booting Linux via Fedora 24's - * grub2-efi on a hard disk. (And no, I don't know why - * this happened, but Linux should still try to boot rather - * panicking early.) - */ - rm_size = real_mode_size_needed(); - if (rm_size && (start + rm_size) < (1<<20) && size >= rm_size) { - set_real_mode_mem(start); - start += rm_size; - size -= rm_size; - } - /* * Don't free memory under 1M for two reasons: * - BIOS might clobber itquoted
+ /* + * Don't free memory under 1M for two reasons: + * - BIOS might clobber it + * - Crash kernel needs it to be reserved + */ + if (start + size < SZ_1M) + continue; + if (start < SZ_1M) { + size -= (SZ_1M - start); + start = SZ_1M; + } + memblock_free_late(start, size); }diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c index 2e1c1bec0f9e..8ea285aca827 100644 --- a/arch/x86/realmode/init.c +++ b/arch/x86/realmode/init.c@@ -29,14 +29,16 @@ void __init reserve_real_mode(void) /* Has to be under 1M so we can execute real-mode AP code. */ mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE); - if (!mem) { + if (!mem) pr_info("No sub-1M memory is available for the trampoline\n"); - return; - } + else + set_real_mode_mem(mem); - memblock_reserve(mem, size); - set_real_mode_mem(mem); - crash_reserve_low_1M(); + /* + * Unconditionally reserve the entire fisrt 1M, see comment in + * setup_arch() + */ + memblock_reserve(0, SZ_1M); } static void sme_sev_setup_real_mode(struct trampoline_header *th)-- 2.28.0
-- Sincerely yours, Mike.