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Fri, 10 Apr 2026 01:00:33 -0700 (PDT) Date: Fri, 10 Apr 2026 09:59:55 +0200 In-Reply-To: <20260410075950.1687350-9-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260410075950.1687350-9-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=3763; i=ardb@kernel.org; h=from:subject; bh=0dtpy6UFjr/qVlazrgUyoaxEm1jrc76faJUnaSEwhU8=; b=owGbwMvMwCVmkMcZplerG8N4Wi2JIfPG2v+9TNaW1mcyLtx/oL1Iz0XN5Xm1ON/GI2+Oh/jKP 9uxdn90RykLgxgXg6yYIovA7L/vdp6eKFXrPEsWZg4rE8gQBi5OAZjIXjOG/3G3i6sOaqR8an0Y ZLCttDHDYVvOze7Hl5ytFr+O7U/luMLIcIj5Ce/8+8wN7FVZdVWZUSK1EtaTWuyilOJa7xXrHxV kAQA= X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260410075950.1687350-14-ardb+git@google.com> Subject: [PATCH 5/7] x86/efi: Simplify real mode trampoline allocation quirk From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Ard Biesheuvel Content-Type: text/plain; charset="UTF-8" From: Ard Biesheuvel To work around a common bug in EFI firmware for x86 systems, Linux reserves all EFI boot services code and data regions until after it has invoked the SetVirtualAddressMap() EFI runtime service. This is needed because those regions may still be accessed by the firmware during that call, even though the EFI spec says that they shouldn't. This includes any boot services data regions below 1M, which might mean that by the time the real mode trampoline is being allocated, all memory below 1M is already exhausted. Commit 5bc653b73182 ("x86/efi: Allocate a trampoline if needed in efi_free_boot_services()") added a quirk to detect this condition, and to make another attempt at allocating the real mode trampoline when freeing those boot services regions again. This is a rather crude hack, which gets in the way of cleanup work on the EFI/x86 memory map handling code. Given that - the real mode trampoline is normally allocated soon after all EFI boot services regions are reserved temporarily, - this allocation logic marks all memory below 1M as reserved, - the trampoline memory is not actually populated until an early initcall, there is actually no need to reserve any boot services regions below 1M, even if they are mapped into the EFI page tables during the call to SetVirtualAddressMap(). So cap the lower bound of the reserved regions to 1M, and fix up the size accordingly when making the reservation. This allows the additional quirk to be dropped entirely. Signed-off-by: Ard Biesheuvel --- arch/x86/platform/efi/quirks.c | 29 ++++---------------- 1 file changed, 6 insertions(+), 23 deletions(-) diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c index 999c9277c49c..ee906c0c46c1 100644 --- a/arch/x86/platform/efi/quirks.c +++ b/arch/x86/platform/efi/quirks.c @@ -324,10 +324,14 @@ void __init efi_reserve_boot_services(void) return; for_each_efi_memory_desc(md) { - u64 start = md->phys_addr; - u64 size = md->num_pages << EFI_PAGE_SHIFT; + u64 start = max(md->phys_addr, SZ_1M); + u64 end = md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT); + u64 size = end - start; bool already_reserved; + if (end <= start) + continue; + if (md->type != EFI_BOOT_SERVICES_CODE && md->type != EFI_BOOT_SERVICES_DATA) continue; @@ -427,7 +431,6 @@ void __init efi_unmap_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) { @@ -448,26 +451,6 @@ void __init efi_unmap_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; - } - /* * With CONFIG_DEFERRED_STRUCT_PAGE_INIT parts of the memory * map are still not initialized and we can't reliably free -- 2.53.0.1213.gd9a14994de-goog