Re: [PATCH 3/3] x86/HVM: correct error code writing during task switch

From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH 3/3] x86/HVM: correct error code writing during task switch
Date: Wed, 23 Nov 2016 01:33:40 -0700	[thread overview]
Message-ID: <58356274020000780012126B@prv-mh.provo.novell.com> (raw)
In-Reply-To: <ba6b3544-f4f8-00ab-5c1c-4f4c81679095@citrix.com>

>>> On 22.11.16 at 17:58, <andrew.cooper3@citrix.com> wrote:
> On 22/11/16 13:56, Jan Beulich wrote:
>> Whether to write 32 or just 16 bits depends on the D bit of the target
>> CS. The width of the stack pointer to use depends on the B bit of the
>> target SS.
>>
>> Also avoid using the no-fault copying routine.
>>
>> Finally avoid using yet another struct segment_register variable here.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -3033,9 +3033,6 @@ void hvm_task_switch(
>>              goto out;
>>      }
>>  
>> -    if ( (tss.trace & 1) && !exn_raised )
>> -        hvm_inject_hw_exception(TRAP_debug, HVM_DELIVER_NO_ERROR_CODE);
>> -
>>      tr.attr.fields.type = 0xb; /* busy 32-bit tss */
>>      hvm_set_segment_register(v, x86_seg_tr, &tr);
>>  
>> @@ -3051,17 +3048,32 @@ void hvm_task_switch(
>>  
>>      if ( errcode >= 0 )
>>      {
>> -        struct segment_register reg;
>>          unsigned long linear_addr;
>> -        regs->esp -= 4;
>> -        hvm_get_segment_register(current, x86_seg_ss, &reg);
>> -        /* Todo: do not ignore access faults here. */
>> -        if ( hvm_virtual_to_linear_addr(x86_seg_ss, &reg, regs->esp,
>> -                                        4, hvm_access_write, 32,
>> +        unsigned int opsz, sp;
>> +
>> +        hvm_get_segment_register(current, x86_seg_cs, &segr);
> 
> You already have current latched in v at this point.

Oh, right - I've blindly modified the old function invocation.

> Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Thanks, Jan

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