Re: [Xen-devel] [PATCH RFC V2 6/6] xen: Handle resumed instruction based on previous mem_event reply

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 07/11/2014 09:36 PM, Andrew Cooper wrote:
> On 11/07/14 16:43, Razvan Cojocaru wrote:
>> In a scenario where a page fault that triggered a mem_event occured,
>> p2m_mem_access_check() will now be able to either 1) emulate the
>> current instruction, or 2) emulate it, but don't allow it to perform
>> any writes.
>>
>> Changes since V1:
>>  - Removed the 'skip' code which required computing the current
>>    instruction length.
>>  - Removed the set_ad_bits() code that attempted to modify the
>>    'accessed' and 'dirty' bits for instructions that the emulator
>>    can't handle at the moment.
>>
>> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>> ---
>>  xen/arch/x86/domain.c          |    5 +++
>>  xen/arch/x86/mm/p2m.c          |   90 
>> ++++++++++++++++++++++++++++++++++++++++
>>  xen/include/asm-x86/domain.h   |    9 ++++
>>  xen/include/public/mem_event.h |   12 +++---
>>  4 files changed, 111 insertions(+), 5 deletions(-)
>>
>> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
>> index e896210..5cd283b 100644
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -407,6 +407,11 @@ int vcpu_initialise(struct vcpu *v)
>>  
>>      v->arch.flags = TF_kernel_mode;
>>  
>> +    /* By default, do not emulate */
>> +    v->arch.mem_event.emulate_flags = 0;
>> +    v->arch.mem_event.gpa = 0;
>> +    v->arch.mem_event.eip = 0;
>> +
>>      rc = mapcache_vcpu_init(v);
>>      if ( rc )
>>          return rc;
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>> index 13fdf78..7aff480 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -1377,6 +1377,7 @@ bool_t p2m_mem_access_check(paddr_t gpa, bool_t 
>> gla_valid, unsigned long gla,
>>  {
>>      struct vcpu *v = current;
>>      unsigned long gfn = gpa >> PAGE_SHIFT;
>> +    unsigned long exit_qualification;
>>      struct domain *d = v->domain;    
>>      struct p2m_domain* p2m = p2m_get_hostp2m(d);
>>      mfn_t mfn;
>> @@ -1384,6 +1385,9 @@ bool_t p2m_mem_access_check(paddr_t gpa, bool_t 
>> gla_valid, unsigned long gla,
>>      p2m_access_t p2ma;
>>      mem_event_request_t *req;
>>      int rc;
>> +    unsigned long eip = guest_cpu_user_regs()->eip;
>> +
>> +    __vmread(EXIT_QUALIFICATION, &exit_qualification);
> 
> This absolutely can't be put into common code.  I presume you haven't
> attempted to run a Xen patched with this on an AMD cpu ?

Indeed, we have not. I think that for a while there wasn't even support
for mem_even when compiling for AMD, so there wasn't really even a choice.

What would be the best way to get that value in a cross-CPU manner?


Thanks,
Razvan Cojocaru

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