Messages in this thread | | | Date | Wed, 5 Sep 2018 10:02:35 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 1/3] x86/boot: Add bit fields into xloadflags for 5-level kernel checking |
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On Tue, 4 Sep 2018, H. Peter Anvin wrote:
> On 09/04/18 01:42, Kirill A. Shutemov wrote: > > > > Switching between 4- and 5-level paging modes (in either direction) > > requires paing disabling. It means the code that does the switching has to > > be under 4G otherwise we would lose control. > > > > We handle the switching correctly in kernel decompression code, but not on > > kexec caller side. > > > > XLF_5LEVEL indicates that kernel decompression code can deal with > > switching between paging modes and it's safe to jump there in 5-level > > paging mode. > > > > As an alternative we can change kexec to switch to 4-level paging mode > > before starting the new kernel. Not sure how hard it will be. > > > > Have a flag saying entering in 5-level mode is fine. However, you really > should support returning to 4-level mode in kexec. It is *much* easier to do > on the caller side as you have total control of memory allocation there.
Works for a regular kexec, but not for starting a crash kernel....
Thanks,
tglx
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