Re: [PATCH v1 4/7] x86/vmx: add do_vmtrace_op

[Michał Leszczyński <michal.leszczynski@xxxxxxx>]

----- 18 cze 2020 o 14:51, Jan Beulich jbeulich@xxxxxxxx napisał(a):

> On 18.06.2020 13:55, Roger Pau Monné wrote:
>> On Thu, Jun 18, 2020 at 01:01:39PM +0200, Michał Leszczyński wrote:
>>> It was previously stated that:
>>>
>>>> PVH or HVM domain
>>>> won't be able to use this interface since it has no way to request the
>>>> mapping of a specific mfn into it's physmap.
>>>
>>> but however, taking LibVMI as an example:
>>>
>>> https://github.com/libvmi/libvmi/blob/c461e20ae88bc62c08c27f50fcead23c27a30f9e/libvmi/driver/xen/xen.c#L51
>>>
>>> An essential abstraction xen_get_memory() relies on xc_map_foreign_range().
>>> Doesn't this mean that it's not usable from PVH or HVM domains, or did I 
>>> got it
>>> all wrong?
>> 
>> That was my fault, so the buffer mfns are assigned to Xen, and then
>> the Xen domain ID is used to map those, which should work on both PV
>> and HVM (or PVH).
>> 
>> I still think using XENMEM_acquire_resource might be better, but I
>> would let others comment.
> 
> +1
> 
> Jan


I'm trying to implement this right now. I've added some very simple code to 
mm.c just for testing:

---

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index e376fc7e8f..aaaefe6d23 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4624,6 +4624,26 @@ int arch_acquire_resource(struct domain *d, unsigned int 
type,
         }
         break;
     }
+
+    case XENMEM_resource_vmtrace_buf:
+    {
+        uint64_t output_base;
+        mfn_t mfn;
+        unsigned int i;
+
+        printk("vmtrace buf acquire\n");
+        output_base = d->vcpu[id]->arch.hvm.vmx.ipt_state->output_base;
+        mfn = mfn_x(output_base >> PAGE_SHIFT);
+
+        rc = 0;
+        for ( i = 0; i < nr_frames; i++ )
+        {
+            __map_domain_page_global(mfn_to_page(mfn + i));
+            mfn_list[i] = mfn + i;
+        }
+
+        break;
+    }
 #endif

     default:

---


and then in my "proctrace" tool I'm trying to acquire it like this:

    fres = xenforeignmemory_map_resource(
        fmem, domid, XENMEM_resource_vmtrace_buf,
        /* vcpu: */ 0, /* frame: */ 0, /* num_frames: */ 128, (void **)&buf,
        PROT_READ, 0);


ioctl fails with "Argument list too long". It works fine when I provide some 
small number of frames (e.g. num_frames: 1 or 32), but doesn't work for any 
larger quantity.

How should I proceed with this? The PT buffer could be large, even up to 4 GB.


Best regards,
Michał Leszczyński
CERT Polska