Adding regress...@leemhuis.info to CC so this regression is tracked. Regards,
Tomeu On 8 November 2017 at 09:37, Tomeu Vizoso <to...@tomeuvizoso.net> wrote: > On 6 November 2017 at 23:01, Tom Lendacky <thomas.lenda...@amd.com> wrote: >> On 11/6/2017 3:41 PM, H. Peter Anvin wrote: >>> >>> On 11/06/17 12:17, Tom Lendacky wrote: >>>> >>>> When crosvm is used to boot a kernel as a VM, the SMP MP-table is found >>>> at physical address 0x0. This causes mpf_base to be set to 0 and a >>>> subsequent "if (!mpf_base)" check in default_get_smp_config() results in >>>> the MP-table not being parsed. Further into the boot this results in an >>>> oops when attempting a read_apic_id(). >>>> >>>> Add a boolean variable that is set to true when the MP-table is found. >>>> Use this variable for testing if the MP-table was found so that even a >>>> value of 0 for mpf_base will result in continued parsing of the MP-table. >>>> >>>> Reported-by: Tomeu Vizoso <to...@tomeuvizoso.net> >>>> Signed-off-by: Tom Lendacky <thomas.lenda...@amd.com> >>> >>> >>> Ahem... did anyone ever tell you that this is an epicly bad idea on your >>> part? The low megabyte of physical memory has very special meaning on >>> x86, and deviating from the standard use of this memory is a *very* >>> dangerous thing to do, and imposing on the kernel a "fake null pointer" >>> requirement that exists only for the convenience of your particular >>> brokenness is not okay. >>> >>> -hpa >> >> >> That was my initial thought... what was something doing down at the start >> of memory. But when I looked at default_find_smp_config() it specifically >> scans the bottom 1K for a an MP-table signature. I was hoping to get some >> feedback as to whether this would really be an acceptable thing to do. So >> I'm good with this patch being rejected, but the change I made in >> >> 5997efb96756 ("x86/boot: Use memremap() to map the MPF and MPC data") >> >> does break something that was working before. > > Do I understand correctly that the best we can do right now is > reverting 5997efb96756? > > Thanks, > > Tomeu