Re: [Xen-devel] [PATCH v2 08/12] x86/altp2m: alternate p2m memory events.

[Ed White <edmund.h.white@xxxxxxxxx>]

On 06/24/2015 09:01 AM, Lengyel, Tamas wrote:
> On Mon, Jun 22, 2015 at 2:56 PM, Ed White <edmund.h.white@xxxxxxxxx> wrote:
> 
>> Add a flag to indicate that a memory event occurred in an alternate p2m
>> and a field containing the p2m index. Allow the response to switch to
>> a different p2m using the same flag and field.
>>
>> Modify p2m_access_check() to handle alternate p2m's.
>>
>> Signed-off-by: Ed White <edmund.h.white@xxxxxxxxx>
>> ---
>>  xen/arch/x86/mm/p2m.c         | 20 +++++++++++++++++++-
>>  xen/include/asm-arm/p2m.h     |  7 +++++++
>>  xen/include/asm-x86/p2m.h     |  4 ++++
>>  xen/include/public/vm_event.h | 13 ++++++++++++-
>>  xen/include/xen/mem_access.h  |  1 +
>>  5 files changed, 43 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>> index 87b4b75..389360a 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -1516,6 +1516,13 @@ void p2m_mem_access_emulate_check(struct vcpu *v,
>>      }
>>  }
>>
>> +void p2m_mem_access_altp2m_check(struct vcpu *v, const
>> vm_event_response_t *rsp)
>> +{
>> +    if ( (rsp->flags & MEM_ACCESS_ALTERNATE_P2M) &&
>> +         altp2mhvm_active(v->domain) )
>> +        p2m_switch_vcpu_altp2m_by_id(v, rsp->u.mem_access.altp2m_idx);
>> +}
>>
> 
> The function should be renamed p2m_altp2m_check as it is not really
> required to use mem_access at all to be able use altp2m. See my comment
> below.
> 
> 
>> +
>>  bool_t p2m_mem_access_check(paddr_t gpa, unsigned long gla,
>>                              struct npfec npfec,
>>                              vm_event_request_t **req_ptr)
>> @@ -1523,7 +1530,7 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned
>> long gla,
>>      struct vcpu *v = current;
>>      unsigned long gfn = gpa >> PAGE_SHIFT;
>>      struct domain *d = v->domain;
>> -    struct p2m_domain* p2m = p2m_get_hostp2m(d);
>> +    struct p2m_domain *p2m = NULL;
>>      mfn_t mfn;
>>      p2m_type_t p2mt;
>>      p2m_access_t p2ma;
>> @@ -1531,6 +1538,11 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned
>> long gla,
>>      int rc;
>>      unsigned long eip = guest_cpu_user_regs()->eip;
>>
>> +    if ( altp2mhvm_active(d) )
>> +        p2m = p2m_get_altp2m(v);
>> +    if ( !p2m )
>> +        p2m = p2m_get_hostp2m(d);
>> +
>>      /* First, handle rx2rw conversion automatically.
>>       * These calls to p2m->set_entry() must succeed: we have the gfn
>>       * locked and just did a successful get_entry(). */
>> @@ -1637,6 +1649,12 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned
>> long gla,
>>          req->vcpu_id = v->vcpu_id;
>>
>>          p2m_vm_event_fill_regs(req);
>> +
>> +        if ( altp2mhvm_active(v->domain) )
>> +        {
>> +            req->flags |= MEM_ACCESS_ALTERNATE_P2M;
>> +            req->u.mem_access.altp2m_idx = vcpu_altp2mhvm(v).p2midx;
>> +        }
>>      }
>>
>>      /* Pause the current VCPU */
>> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
>> index 63748ef..b31dd6f 100644
>> --- a/xen/include/asm-arm/p2m.h
>> +++ b/xen/include/asm-arm/p2m.h
>> @@ -109,6 +109,13 @@ void p2m_mem_access_emulate_check(struct vcpu *v,
>>      /* Not supported on ARM. */
>>  }
>>
>> +static inline
>> +void p2m_mem_access_altp2m_check(struct vcpu *v,
>> +                                const mem_event_response_t *rsp)
>> +{
>> +    /* Not supported on ARM. */
>> +}
>> +
>>  #define p2m_is_foreign(_t)  ((_t) == p2m_map_foreign)
>>  #define p2m_is_ram(_t)      ((_t) == p2m_ram_rw || (_t) == p2m_ram_ro)
>>
>> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
>> index 16fd523..d84da33 100644
>> --- a/xen/include/asm-x86/p2m.h
>> +++ b/xen/include/asm-x86/p2m.h
>> @@ -762,6 +762,10 @@ bool_t p2m_find_altp2m_by_eptp(struct domain *d,
>> uint64_t eptp, unsigned long *i
>>  /* Switch alternate p2m for a single vcpu */
>>  bool_t p2m_switch_vcpu_altp2m_by_id(struct vcpu *v, uint16_t idx);
>>
>> +/* Check to see if vcpu should be switched to a different p2m. */
>> +void p2m_mem_access_altp2m_check(struct vcpu *v,
>> +                                 const vm_event_response_t *rsp);
>> +
>>  /*
>>   * p2m type to IOMMU flags
>>   */
>> diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
>> index 577e971..b492f65 100644
>> --- a/xen/include/public/vm_event.h
>> +++ b/xen/include/public/vm_event.h
>> @@ -149,13 +149,24 @@ struct vm_event_regs_x86 {
>>   * potentially having side effects (like memory mapped or port I/O)
>> disabled.
>>   */
>>  #define MEM_ACCESS_EMULATE_NOWRITE      (1 << 7)
>> +/*
>> + * This flag can be set in a request or a response
>> + *
>> + * On a request, indicates that the event occurred in the alternate p2m
>> specified by
>> + * the altp2m_idx request field.
>> + *
>> + * On a response, indicates that the VCPU should resume in the alternate
>> p2m specified
>> + * by the altp2m_idx response field if possible.
>> + */
>> +#define MEM_ACCESS_ALTERNATE_P2M        (1 << 8)
>>
> 
> This definition should be renamed VM_EVENT_FLAG_ALTERNATE_P2M and moved to
> the appropriate location. It should also be checked for all events, not
> just for mem_access, similar to how VM_EVENT_FLAG_VCPU_PAUSED is checked
> for, as we might want to switch views in response to a variety of events.
> Right now I worked around this be specifying the response to a singlestep
> event as if it was a response to a mem_access one, but that's very hackish.

Good points. I'll do as you suggest.

Ed


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