On Wed, Nov 29, 2017 at 04:49:08PM +0100, Borislav Petkov wrote: > On Sat, Nov 11, 2017 at 01:06:41AM +0300, Kirill A. Shutemov wrote: > > Hi Ingo, > > > > Here's updated changes that prepare the code to boot-time switching between > > paging modes and handle booting in 5-level mode when bootloader put kernel > > image above 4G, but haven't enabled 5-level paging for us. > > Btw, if I enable CONFIG_X86_5LEVEL with 4.15-rc1 on an AMD box, the box > triple-faults and ends up spinning in a reboot loop. Even though it > should say: > > early console in setup code > This kernel requires the following features not present on the CPU: > la57 > Unable to boot - please use a kernel appropriate for your CPU. > > and halt. > > A kvm guest still does that but baremetal triple-faults. > > Ideas?
Looks like we call check_cpuflags() too late. 5-level paging gets enabled before image decompression started. For qemu/kvm it works because it's supported in softmmu, even if not advertised in cpuid. I'm not sure if it worth fixing on its own. I would rather get boot-time switching code upstream sooner. It will get problem go away naturally. -- Kirill A. Shutemov
