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

[Andrew Cooper <andrew.cooper3@citrix.com>]

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@bitdefender.com>
> ---
>  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 ?

~Andrew