Re: [Xen-devel] [PATCH v3] mem_access: sanitize code around sending vm_event request

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.08.16 at 20:41, <tamas.lengyel@xxxxxxxxxxxx> wrote:
> The two functions monitor_traps and mem_access_send_req duplicate some of the
> same functionality. The mem_access_send_req however leaves a lot of the
> standard vm_event fields to be filled by other functions.
> 
> Remove mem_access_send_req() completely, making use of monitor_traps() to 
> put
> requests into the monitor ring.  This in turn causes some cleanup around the
> old callsites of mem_access_send_req(). We also update monitor_traps to now
> include setting the common vcpu_id field so that all other call-sites can 
> ommit
> this step.
> 
> Finally, this change identifies that errors from mem_access_send_req() were
> never checked.  As errors constitute a problem with the monitor ring,
> crashing the domain is the most appropriate action to take.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> 
> v3: reduce the code movement and sanitization performed to a minimum

Doesn't this invalidate prior reviews and acks?

> @@ -1846,11 +1846,15 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
> long gla,
>                  }
>              }
>  
> -            if ( p2m_mem_access_check(gpa, gla, npfec, &req_ptr) )
> -            {
> +            sync = p2m_mem_access_check(gpa, gla, npfec, &req_ptr);
> +
> +            if ( !sync )
>                  fall_through = 1;
> -            } else {
> -                /* Rights not promoted, vcpu paused, work here is done */
> +            else
> +            {
> +                /*
> +                 * Rights not promoted (aka. sync event), work here is done
> +                 */

Comment style.

> @@ -1750,23 +1745,12 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned 
> long gla,
>          req->u.mem_access.flags |= npfec.read_access    ? MEM_ACCESS_R : 0;
>          req->u.mem_access.flags |= npfec.write_access   ? MEM_ACCESS_W : 0;
>          req->u.mem_access.flags |= npfec.insn_fetch     ? MEM_ACCESS_X : 0;
> -        req->vcpu_id = v->vcpu_id;
> -
> -        vm_event_fill_regs(req);
> -
> -        if ( altp2m_active(v->domain) )
> -        {
> -            req->flags |= VM_EVENT_FLAG_ALTERNATE_P2M;
> -            req->altp2m_idx = vcpu_altp2m(v).p2midx;
> -        }
>      }
>  
> -    /* Pause the current VCPU */
> -    if ( p2ma != p2m_access_n2rwx )
> -        vm_event_vcpu_pause(v);
> -
> -    /* VCPU may be paused, return whether we promoted automatically */
> -    return (p2ma == p2m_access_n2rwx);
> +    /*
> +     * Return whether vCPU pause is required (aka. sync event)
> +     */

Again.

> +    return (p2ma != p2m_access_n2rwx);

Pointless parentheses.

Jan


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