On 03/12/19 at 06:30pm, Baoquan He wrote: > This is v3 post. > > The original v1 post can be found here: > http://lkml.kernel.org/r/20180829141624.13985-1-...@redhat.com > > Later a v1 RESEND version: > http://lkml.kernel.org/r/20190125022817.29506-1-...@redhat.com > > V2 post is here: > http://lkml.kernel.org/r/20190312005004.19182-1-...@redhat.com > > This patchset is trying to fix several issues for kexec/kdump when > dynamic switching of paging mode is enabled in x86_64. The current > kernel supports 5-level paging mode, and supports dynamically choosing > paging mode during bootup according to kernel image, hardware and > kernel parameter setting. This flexibility brings several issues for > kexec/kdump: > > Issues: > 1) > Dynamic switching between paging mode requires code change in target > kernel. So we can't kexec jump from 5-level kernel to old 4-level > kernel which lacks the code change. > > 2) > Switching from 5-level paging to 4-level paging kernel would fail, if > kexec() put kernel image above 64TiB of memory. > > 3) > Kdump jumping has similar issue as 2). This require us to only > reserve crashkernel below 64TB, otherwise jumping from 5-level to > 4-level kernel will fail. > > Note: > Since we have two interfaces kexec_load() and kexec_file_load() to load > kexec/kdump kernel, handling for them is a little different. For > kexec_load(), most of the loading job is done in user space utility > kexec_tools. However, for kexec_file_load(), most of the loading codes > have moved into kernel because of kernel image verification. > > Fixes: > a) For issue 1), we need check if XLF_5LEVEL is set, otherwise error out > a message. > -This need be done in both kernel and kexec_tools utility. > -Patch 2/3 is the handling of kernel part. > -Will post user space patch to kexec mailing list later. > > b) For issue 2), we need check if both XLF_5LEVEL and XLF_5LEVEL_ENABLED > are set, otherwise error out a message. > -This only need be done in kexec_tools utility. Because for > kexec_file_load(), the current code searches area to put kernel from > bottom to up in system RAM, we usually can always find an area below > 4 GB, no need to worry about 5-level kernel jumping to 4-level > kernel. While for kexec_load(), it's top down seraching area for kernel > loading, and implemented in user space. We need make sure that > 5-level kernel find an area under 64 TB for a kexec-ed kernel of > 4-level.
This paragraph is used to explain why XLF_5LEVEL_ENABLED is not checked in kernel. I will add these information to log of patch 1/3. > -Will post user space patch to kexec mailing list later. > > c) For issues 3), just limit kernel to reserve crashkernel below 64 TB. > -This only need be done in kernel. > -It doesn't need to check bit XLF_5LEVEL or XLF_5LEVEL_ENABLED, we > just simply limit it below 64 TB which should be enough. Because > crashernel is reserved during the 1st kernel's bootup, we don't know > what kernel will be loaded for kdump usage. > -Patch 3/3 handles this. > > Concerns from reviewing comments: > 1) > In v1, hpa raised concern that why the paging mode checking is not done > before kexec jumping, the discussion can be found here: > > http://lkml.kernel.org/r/alpine.deb.2.21.1809051002020.1...@nanos.tec.linutronix.de > > As tglx said, it might be not doable for kdump since kdump kernel's > reserved crashkernel region only owns a portion of memory, may > be above 4G; and might be not safer to do paging mode checking and > switching thing after crash. > > 2) > In v1 RESEND post, tglx asked why only bit XLF_5LEVEL is checked, even > though two bits XLF_5LEVEL or XLF_5LEVEL_ENABLED added. So add more > words to explain it in *Fixes* b). > > Changelog: > v2->v3: > Change the constant to match the notation for the rest of defines as > Kirill suggested; > v1->v2: > Correct the subject of patch 1 according to tglx's comment; > Add more information to cover-letter to address reviewers' concerns; > > Baoquan He (3): > x86/boot: Add xloadflags bits for 5-level kernel checking > x86/kexec/64: Error out if try to jump to old 4-level kernel from > 5-level kernel > x86/kdump/64: Change the upper limit of crashkernel reservation > > arch/x86/boot/header.S | 12 +++++++++++- > arch/x86/include/uapi/asm/bootparam.h | 2 ++ > arch/x86/kernel/kexec-bzimage64.c | 5 +++++ > arch/x86/kernel/setup.c | 18 ++++++++++++++---- > 4 files changed, 32 insertions(+), 5 deletions(-) > > -- > 2.17.2 >