Re: EFI Xen unstable crashes on Dell E6410 when calling efi_get_time.

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 22/10/14 01:29, Marcos E. Matsunaga wrote:
> I went out and got the serial cable. Attached is the full output.
>
>
> On 10/21/2014 05:06 PM, Marcos E. Matsunaga wrote:
>> Folks,
>>
>> I am trying to boot Xen using efibootmgr on a Dell E6410 laptop with
>> 4GB RAM, running an Intel I5 dual core with VT and all the
>> virtualization options enabled.
>>
>> It crashes almost immediately. I am working on getting the serial
>> console up so that I can get a more detailed stack.
>>
>> A screenshot of the console is attached.
>>
>> The xen.cfg file is:
>>
>> [global]
>> default=xen
>>
>> [xen]
>> options=console=vga,com1 com1=115200,8n1 dom0_max_vcpus=2 vga="qxl"
>> kernel=vmlinuz-3.8.13-48.el7uek.Other_EFI_v1.x86_64
>> root=UUID=917bfc7f-8d9c-4acf-a98a-a9f558daccf2  ro console=hvc0
>> enforcing=0 biosdevname=0 earlyprintk=xen nomodeset
>> ramdisk=initramfs-3.8.13-48.el7uek.Other_EFI_v1.x86_64.img
>>
>>
>> The codepath is "(gdb) x/20i get_cmos_time
>>    0xffff82d080188825 <get_cmos_time>:  push   %rbp
>>    0xffff82d080188826 <get_cmos_time+1>:        mov %rsp,%rbp
>>    0xffff82d080188829 <get_cmos_time+4>:        push   %r12
>>    0xffff82d08018882b <get_cmos_time+6>:        push   %rbx
>>    0xffff82d08018882c <get_cmos_time+7>:        cmpb
>> $0x0,0xb620d(%rip)        # 0xffff82d08023ea40 <efi_enabled>
>>    0xffff82d080188833 <get_cmos_time+14>:       je 0xffff82d080188843
>> <get_cmos_time+30>
>>    0xffff82d080188835 <get_cmos_time+16>:       callq
>> 0xffff82d080100069 <efi_get_time>"
>>
>

Ok - there are two separate bugs here.

The first is that we call into the efi runtime via efi_rs->GetTime, and
a pagefault happens for the instruction at 0x00000000db25a33d for the
virtual address 0x00000000fed1f410

The memory map looks quite weird, but the faulting address is covered in
this range.

(XEN)  00000fed1c000-00000fed1ffff type=11 attr=8000000000000000

So I would expect it to be mapped into the EFI pagetables.

The EFI code is a mix of #ifdefs.  Can you confirm whether you are
compiling with USE_SET_VIRTUAL_ADDRESS_MAP or not?


The second is that once the pagefault has happened, we trap back into
Xen and attempt to do a pagetable walk, falling over an assertion in
map_domain_page().

For EFI calls, we run on the efi pagetables, not the idle pagetables, so
I am not surprised that the assertion has failed.  I suspect that the
pagefault hander for hypervisor faults needs to become wise to the fact
that we may receive a fault when calling into the firmware.  As all the
efi pagetables are xenheap pages, there is nothing conceptually wrong
with using map_domain_page() to do the walk.

~Andrew