Re: [PATCH] x86/smpboot: Unconditionally call memguard_unguard_stack() in cpu_smpboot_free()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/10/2020 14:16, Jan Beulich wrote:
> On 05.10.2020 14:23, Andrew Cooper wrote:
>> --- a/xen/arch/x86/smpboot.c
>> +++ b/xen/arch/x86/smpboot.c
>> @@ -971,16 +971,16 @@ static void cpu_smpboot_free(unsigned int cpu, bool 
>> remove)
>>      if ( IS_ENABLED(CONFIG_PV32) )
>>          FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu));
>>  
>> +    if ( stack_base[cpu] )
>> +        memguard_unguard_stack(stack_base[cpu]);
>> +
>>      if ( remove )
>>      {
>>          FREE_XENHEAP_PAGE(per_cpu(gdt, cpu));
>>          FREE_XENHEAP_PAGE(idt_tables[cpu]);
>>  
>>          if ( stack_base[cpu] )
>> -        {
>> -            memguard_unguard_stack(stack_base[cpu]);
>>              FREE_XENHEAP_PAGES(stack_base[cpu], STACK_ORDER);
>> -        }
>>      }
>>  }
> In my initial reply to Marek's report I did suggest putting the fix
> in the alloc path in order to keep the pages "guarded" while the CPU
> is parked

In which case you should have identified that bug explicitly.

Because I can't read your mind while fixing the other real bugs in your
suggestion.

~Andrew