Re: [Xen-devel] [PATCH-for-4.11] xpti: fix bug in double fault handling

[Juergen Gross <jgross@xxxxxxxx>]

On 23/04/18 14:11, Jan Beulich wrote:
>>>> On 23.04.18 at 13:37, <jgross@xxxxxxxx> wrote:
>> When entering the hypervisor via the double fault handler resetting
>> xen_cr3 was missing. This led to switching to pv_cr3 when returning
>> from the next following interrupt, e.g. after re-enabling interrupts
>> in machine_restart().
> 
> Pointing at bad behavior to justify a change is not very helpful, I think.
> Andrew's argument of exception handling wanting to continue to work
> even after a #DF is a better one imo.

Okay.

> 
>> --- a/tools/firmware/xen-dir/shim.config
>> +++ b/tools/firmware/xen-dir/shim.config
>> @@ -1,6 +1,6 @@
>>  #
>>  # Automatically generated file; DO NOT EDIT.
>> -# Xen/x86 4.11-unstable Configuration
>> +# Xen/x86 4.11-rc Configuration
>>  #
>>  CONFIG_X86_64=y
>>  CONFIG_X86=y
> 
> Stray change?

Oh, that one again. Sorry. Maybe we should really take my related
patch to avoid issues like this one.

> 
>> --- a/xen/arch/x86/x86_64/entry.S
>> +++ b/xen/arch/x86/x86_64/entry.S
>> @@ -772,6 +772,7 @@ ENTRY(double_fault)
>>          jns   .Ldblf_cr3_load
>>          neg   %rbx
>>  .Ldblf_cr3_load:
>> +        movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
>>          mov   %rbx, %cr3
>>  .Ldblf_cr3_okay:
> 
> Just like for the other code paths this write should be after the CR3 load,
> or else NMI or #MC occurring between the two would fail to update CR3.

Aah, right.

Will send V2 soon.


Juergen


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