[Xen-devel] Regression between Xen 4.6.0 and 4.7.0, Direct kernel boot on a qemu-xen and seabios HVM guest doesn't work anymore.

[linux@xxxxxxxxxxxxxx]

Today i tried to switch some of my HVM guests (qemu-xen) from booting of 
a kernel *inside* the guest, to a dom0 supplied kernel, which is 
described as "Direct Kernel Boot" here: 
https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html :
    Direct Kernel Boot

    Direct kernel boot allows booting directly from a kernel and initrd 
stored in the host physical
    machine OS, allowing command line arguments to be passed directly. 
PV guest direct kernel boot
    is supported. HVM guest direct kernel boot is supported with 
limitation (it's supported when
    using qemu-xen and default BIOS 'seabios'; not supported in case of 
stubdom-dm and old rombios.)
    kernel="PATHNAME"    Load the specified file as the kernel image.
    ramdisk="PATHNAME"   Load the specified file as the ramdisk.

But qemu fails to start, output appended below.

I tested with:
- current Xen-unstable, which fails.
- xen-stable-4.7.0 release, which fails.
- xen-stable-4.6.0 release, works fine.

So it's a regression somewhere between 4.6.0 and 4.7.0, but hopefully 
someone has a hunch before trying to do a whole bisect between those two 
releases.
--
Sander

From the qemu log:

qemu: hardware error: xen: failed to populate ram at 40050000
CPU #0:
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000663
ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0000 00000000 0000ffff 00009300
CS =f000 ffff0000 0000ffff 00009b00
SS =0000 00000000 0000ffff 00009300
DS =0000 00000000 0000ffff 00009300
FS =0000 00000000 0000ffff 00009300
GS =0000 00000000 0000ffff 00009300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 0000ffff
IDT=     00000000 0000ffff
CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000
DR6=ffff0ff0 DR7=00000400
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 
XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 
XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 
XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 
XMM07=00000000000000000000000000000000
CPU #1:
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000663
ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=1
ES =0000 00000000 0000ffff 00009300
CS =f000 ffff0000 0000ffff 00009b00
SS =0000 00000000 0000ffff 00009300
DS =0000 00000000 0000ffff 00009300
FS =0000 00000000 0000ffff 00009300
GS =0000 00000000 0000ffff 00009300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 0000ffff
IDT=     00000000 0000ffff
CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000
DR6=ffff0ff0 DR7=00000400
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 
XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 
XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 
XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 
XMM07=00000000000000000000000000000000
CPU #2:
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000663
ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=1
ES =0000 00000000 0000ffff 00009300
CS =f000 ffff0000 0000ffff 00009b00
SS =0000 00000000 0000ffff 00009300
DS =0000 00000000 0000ffff 00009300
FS =0000 00000000 0000ffff 00009300
GS =0000 00000000 0000ffff 00009300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 0000ffff
IDT=     00000000 0000ffff
CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000
DR6=ffff0ff0 DR7=00000400
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 
XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 
XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 
XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 
XMM07=00000000000000000000000000000000
CPU #3:
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000663
ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=1
ES =0000 00000000 0000ffff 00009300
CS =f000 ffff0000 0000ffff 00009b00
SS =0000 00000000 0000ffff 00009300
DS =0000 00000000 0000ffff 00009300
FS =0000 00000000 0000ffff 00009300
GS =0000 00000000 0000ffff 00009300
LDT=0000 00000000 0000ffff 00008200
TR =0000 00000000 0000ffff 00008b00
GDT=     00000000 0000ffff
IDT=     00000000 0000ffff
CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000
DR6=ffff0ff0 DR7=00000400
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000 
XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000 
XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000 
XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000 
XMM07=00000000000000000000000000000000

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