From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54236) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gL6d5-0006Qu-7l for qemu-devel@nongnu.org; Fri, 09 Nov 2018 08:15:20 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gL6d0-0004sG-Gk for qemu-devel@nongnu.org; Fri, 09 Nov 2018 08:15:19 -0500 Received: from mga03.intel.com ([134.134.136.65]:44350) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gL6cw-0004i7-S6 for qemu-devel@nongnu.org; Fri, 09 Nov 2018 08:15:12 -0500 References: <1541674784-25936-1-git-send-email-lizhijian@cn.fujitsu.com> <1541674784-25936-2-git-send-email-lizhijian@cn.fujitsu.com> <20181109072015.GA86700@gmail.com> <38905d35-29af-b522-1629-b13e98a47a42@intel.com> From: Li Zhijian Message-ID: <01ae76b5-bc70-7859-91e3-7e60e3cca247@intel.com> Date: Fri, 9 Nov 2018 21:11:17 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Subject: Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juergen Gross , Ingo Molnar , Li Zhijian Cc: Peter Maydell , x86@kernel.org, hpa@zytor.com, bp@alien8.de, mingo@redhat.com, tglx@linutronix.de, QEMU Developers , Philip Li , linux-kernel@vger.kernel.org, Linus Torvalds , Peter Zijlstra , Kees Cook Just noticed that there is a field xloadflags at recent protocol 60 Protocol 2.12: (Kernel 3.8) Added the xloadflags field and extension fields 61 to struct boot_params for loading bzImage and ramdisk 62 above 4G in 64bit. [snip] 617 Field name: xloadflags 618 Type: read 619 Offset/size: 0x236/2 620 Protocol: 2.12+ 621 622 This field is a bitmask. 623 624 Bit 0 (read): XLF_KERNEL_64 625 - If 1, this kernel has the legacy 64-bit entry point at 0x200. 626 627 Bit 1 (read): XLF_CAN_BE_LOADED_ABOVE_4G 628 - If 1, kernel/boot_params/cmdline/ramdisk can be above 4G. 629 maybe we can reuse this field and append a new Bit 5 XLF_INITRD_SIZE_4G or such thanks Zhijian On 11/9/2018 6:04 PM, Juergen Gross wrote: > On 09/11/2018 10:57, Li Zhijian wrote: >> On 11/9/2018 3:20 PM, Ingo Molnar wrote: >>> * Li Zhijian wrote: >>> >>>>> If the kernel initrd creation process creates an initrd which >>>>> is larger than 2GB and also claims that it can't be placed >>>>> with any part of it above 2GB, then that sounds like a bug >>>>> in the initrd creation process... >>>> Exactly, it's a real problem. >>>> >>>> Add x86 maintainers and LKML: >>>> >>>> The background is that QEMU want to support up to 4G initrd. but >>>> linux header ( >>>> initrd_addr_max field) only allow 2G-1. >>>> Is one of the below approaches reasonable: >>>> 1) change initrd_addr_max to 4G-1 directly >>>> simply(arch/x86/boot/header.S)? >>>> 2) lie QEMU bootloader the initrd_addr_max is 4G-1 even though header >>>> said 2G-1 >>>> 3) any else >>> A 10 years old comment from hpa says: >>> >>>    initrd_addr_max: .long 0x7fffffff >>>                                          # (Header version 0x0203 or >>> later) >>>                                          # The highest safe address for >>>                                          # the contents of an initrd >>>                                          # The current kernel allows >>> up to 4 GB, >>>                                          # but leave it at 2 GB to avoid >>>                                          # possible bootloader bugs. >>> >>> To avoid the potential of bugs lurking in dozens of major and hundreds of >>> minor iterations of various Linux bootloaders I'd prefer a real solution >>> and extend it - because if there's a 2GB initrd for some weird reason >>> today there might be a 4GB one in two years. >> thank a lots. that's amazing. >> >> >>> The real solution would be to: >>> >>>   - Extend the boot protocol with a 64-bit field, named initrd_addr64_max >>>     or such. >>>   - We don't change the old field - but if the new field is set by new >>>     kernels then new bootloaders can use that as a new initrd_addr64_max >>>     value. (or reject to load the kernel if the address is too high.) >>> >>>   - The kernel build should also emit a warning when building larger than >>>     2GB initrds, with a list of bootloaders that support the new >>> protocol. >> Actually i just knew QEMU(Seabios + optionrom(linuxboot_dma.bin)) can >> support ~4GB initrd so far. >> >> i just drafted at patch to add this field. could you have a look. >> another patch which is to document initrd_addr64_max is ongoing. >> >> commit db463ac9c1975f115d1ce2acb82d530c2b63b888 >> Author: Li Zhijian >> Date:   Fri Nov 9 17:24:14 2018 +0800 >> >>     x86: Add header field initrd_addr64_max >>         Years ago, kernel had support load ~4GB initrd. But for some >> weird reasons ( >>     avoid possible bootloader bugs), it only allow leave initrd under >> 2GB address >>     space(see initrd_addr_max fild at arch/x86/boot/header.S). >>         So modern bootloaders have not chance to load >=2G initrd >> previously. >>         To avoid the potential of bugs lurking in dozens of major and >> hundreds of >>     minor iterations of various Linux bootloaders. Ingo suggests to add >> a new field >>     initrd_addr64_max. If bootloader believes that it can load initrd to >>> =2G >>     address space, it can use initrd_addr64_max as the maximum loading >> address in >>     stead of the old field initrd_addr_max. >> >> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S >> index 4c881c8..5fc3ebe 100644 >> --- a/arch/x86/boot/header.S >> +++ b/arch/x86/boot/header.S >> @@ -300,7 +300,7 @@ _start: >>         # Part 2 of the header, from the old setup.S >> >>                 .ascii  "HdrS"          # header signature >> -               .word   0x020e          # header version number (>= 0x0105) >> +               .word   0x020f          # header version number (>= 0x0105) >>                                         # or else old loadlin-1.5 will >> fail) >>                 .globl realmode_swtch >>  realmode_swtch:        .word   0, 0            # default_switch, SETUPSEG >> @@ -562,6 +562,12 @@ acpi_rsdp_addr:            .quad 0 >> # 64-bit physical pointer to the >>                                                 # ACPI RSDP table, added >> with >>                                                 # version 2.14 >> >> +#ifdef CONFIG_INITRD_SIZE_4GB >> +initrd_addr64_max:     .quad 0xffffffff        # allow ~4G initrd since >> 2.15 >> +#else >> +initrd_addr64_max:     .quad 0 > Shouldn't this be 0x7fffffff? > > And please update Documentation/x86/boot.txt > > > Juergen