linux-kernel - Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

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Date:	Tue, 15 Jul 2014 11:45:36 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

On 07/15/2014 11:38 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
>> Xen doesn't call start_secondary.
> Duh!
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>> ---
>>
>> espfix still doesn't seem to work on Xen (it goes boom in some way that
>> I don't understand right now), but initializing all CPUs instead of just
>> one of them seems like a good start.
>>
>> ISTM the right fix is probably to shove the espfix logic into
>> native_iret and to tweak the paravirt logic so that native_iret always
>> gets invoked.  I suspect that Xen will need its own implementation of
>> espfix64 in the hypervisor and that, ultimately, someone may want to
>> stop initializing espfix64 at all on Xen guests.
> I think just disallowing would be preferrable.

I've been looking at sigreturn_64 and it seems to be crashing dom0 (with 
both mine and your patches). In kprobe_int3_handler().


-boris

>
> Thanks for posting this patch!
>>   arch/x86/xen/smp.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
>> index 7005974..eea9bcc 100644
>> --- a/arch/x86/xen/smp.c
>> +++ b/arch/x86/xen/smp.c
>> @@ -23,6 +23,7 @@
>>   #include <asm/desc.h>
>>   #include <asm/pgtable.h>
>>   #include <asm/cpu.h>
>> +#include <asm/espfix.h>
>>   
>>   #include <xen/interface/xen.h>
>>   #include <xen/interface/vcpu.h>
>> @@ -85,6 +86,13 @@ static void cpu_bringup(void)
>>   
>>   	xen_setup_cpu_clockevents();
>>   
>> +	/*
>> +	 * Enable the espfix hack for this CPU
>> +	 */
>> +#ifdef CONFIG_X86_ESPFIX64
>> +	init_espfix_ap();
>> +#endif
>> +
>>   	notify_cpu_starting(cpu);
>>   
>>   	set_cpu_online(cpu, true);
>> -- 
>> 1.9.3
>>

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