From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.skyhub.de ([2a01:4f8:190:11c2::b:1457]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lnduc-00BdYi-T0 for kexec@lists.infradead.org; Mon, 31 May 2021 09:08:45 +0000 Date: Mon, 31 May 2021 11:08:32 +0200 From: Borislav Petkov Subject: Re: [PATCH v2] x86/efi: unconditionally hold the whole low-1MB memory regions Message-ID: References: <20210531090023.16471-1-lijiang@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210531090023.16471-1-lijiang@redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Lianbo Jiang , Mike Rapoport Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, kexec@lists.infradead.org, ardb@kernel.org, dvhart@infradead.org, andy@infradead.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, luto@amacapital.net, bhe@redhat.com, dyoung@redhat.com + Mike. On Mon, May 31, 2021 at 05:00:23PM +0800, Lianbo Jiang wrote: > Some sub-1MB memory regions may be reserved by EFI boot services, and the > memory regions will be released later in the efi_free_boot_services(). > > Currently, always reserve all sub-1MB memory regions when the crashkernel > option is specified, but unfortunately EFI boot services may have already > reserved some sub-1MB memory regions before the crash_reserve_low_1M() is > called, which makes that the crash_reserve_low_1M() only own the > remaining sub-1MB memory regions, not all sub-1MB memory regions, because, > subsequently EFI boot services will free its own sub-1MB memory regions. > Eventually, DMA will be able to allocate memory from the sub-1MB area and > cause the following error: > > crash> kmem -s |grep invalid > kmem: dma-kmalloc-512: slab: ffffd52c40001900 invalid freepointer: ffff9403c0067300 > kmem: dma-kmalloc-512: slab: ffffd52c40001900 invalid freepointer: ffff9403c0067300 > crash> vtop ffff9403c0067300 > VIRTUAL PHYSICAL > ffff9403c0067300 67300 --->The physical address falls into this range [0x0000000000063000-0x000000000008efff] > > kernel debugging log: > ... > [ 0.008927] memblock_reserve: [0x0000000000010000-0x0000000000013fff] efi_reserve_boot_services+0x85/0xd0 > [ 0.008930] memblock_reserve: [0x0000000000063000-0x000000000008efff] efi_reserve_boot_services+0x85/0xd0 > ... > [ 0.009425] memblock_reserve: [0x0000000000000000-0x00000000000fffff] crash_reserve_low_1M+0x2c/0x49 > ... > [ 0.010586] Zone ranges: > [ 0.010587] DMA [mem 0x0000000000001000-0x0000000000ffffff] > [ 0.010589] DMA32 [mem 0x0000000001000000-0x00000000ffffffff] > [ 0.010591] Normal [mem 0x0000000100000000-0x0000000c7fffffff] > [ 0.010593] Device empty > ... > [ 8.814894] __memblock_free_late: [0x0000000000063000-0x000000000008efff] efi_free_boot_services+0x14b/0x23b > [ 8.815793] __memblock_free_late: [0x0000000000010000-0x0000000000013fff] efi_free_boot_services+0x14b/0x23b > > To fix the above issues, let's hold the whole low-1M memory regions > unconditionally in the efi_free_boot_services(). > > Signed-off-by: Lianbo Jiang > --- > Background(copy from bhe's comment in the patch v1): > > Kdump kernel also need go through real mode code path during bootup. It > is not different than normal kernel except that it skips the firmware > resetting. So kdump kernel needs low 1M as system RAM just as normal > kernel does. Here we reserve the whole low 1M with memblock_reserve() > to avoid any later kernel or driver data reside in this area. Otherwise, > we need dump the content of this area to vmcore. As we know, when crash > happened, the old memory of 1st kernel should be untouched until vmcore > dumping read out its content. Meanwhile, kdump kernel need reuse low 1M. > In the past, we used a back up region to copy out the low 1M area, and > map the back up region into the low 1M area in vmcore elf file. In > 6f599d84231fd27 ("x86/kdump: Always reserve the low 1M when the crashkernel > option is specified"), we changed to lock the whole low 1M to avoid > writting any kernel data into, like this we can skip this area when > dumping vmcore. > > Above is why we try to memblock reserve the whole low 1M. We don't want > to use it, just don't want anyone to use it in 1st kernel. > > > arch/x86/platform/efi/quirks.c | 32 +++++++++++++++----------------- > 1 file changed, 15 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c > index 7850111008a8..840b7e3b3d48 100644 > --- a/arch/x86/platform/efi/quirks.c > +++ b/arch/x86/platform/efi/quirks.c > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -409,7 +410,7 @@ 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; > + unsigned long long end = start + size; > > if (md->type != EFI_BOOT_SERVICES_CODE && > md->type != EFI_BOOT_SERVICES_DATA) { > @@ -431,23 +432,20 @@ 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.) > + * The sub-1MB memory may be within the range[0, SZ_1M] > + * or across the low-1M memory boundary. Let's handle > + * these two cases and hold the whole low-1M memory > + * unconditionally. > */ > - 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; > + if (start < SZ_1M) { > + /* Within the range[0, SZ_1M] */ > + if (end <= SZ_1M) > + continue; > + else { > + /* Across the low-1M memory boundary */ > + size -= (SZ_1M - start); > + start = SZ_1M; > + } > } > > memblock_free_late(start, size); > -- I don't think this will be needed when this here happens: https://lkml.kernel.org/r/YK%2Bgv0vDfLVD7Sqp@kernel.org -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec