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Re: [Xen-devel] [PATCH 02/18] arm/altp2m: Add first altp2m HVMOP stubs.



Hello Sergej,

On 04/07/16 12:45, Sergej Proskurin wrote:
+static int do_altp2m_op(XEN_GUEST_HANDLE_PARAM(void) arg)
+{
+    struct xen_hvm_altp2m_op a;
+    struct domain *d = NULL;
+    int rc = 0;
+
+    if ( !hvm_altp2m_supported() )
+        return -EOPNOTSUPP;
+
+    if ( copy_from_guest(&a, arg, 1) )
+        return -EFAULT;
+
+    if ( a.pad1 || a.pad2 ||
+         (a.version != HVMOP_ALTP2M_INTERFACE_VERSION) ||
+         (a.cmd < HVMOP_altp2m_get_domain_state) ||
+         (a.cmd > HVMOP_altp2m_change_gfn) )
+        return -EINVAL;
+
+    d = (a.cmd != HVMOP_altp2m_vcpu_enable_notify) ?
+        rcu_lock_domain_by_any_id(a.domain) : rcu_lock_current_domain();
+
+    if ( d == NULL )
+        return -ESRCH;
+
+    if ( (a.cmd != HVMOP_altp2m_get_domain_state) &&
+         (a.cmd != HVMOP_altp2m_set_domain_state) &&
+         !d->arch.altp2m_active )
+    {
+        rc = -EOPNOTSUPP;
+        goto out;
+    }
+
+    if ( (rc = xsm_hvm_altp2mhvm_op(XSM_TARGET, d)) )
+        goto out;

I think this is the best place to ask a couple of questions related to who can access altp2m. Based on this call, a guest is allowed to manage its own altp2m. Can you explain why we would want a guest to do that?

Also, I have noticed that a guest is allowed to disable ALTP2M on ARM because it set any param (x86 has some restriction on it). Similarly, the ALTP2M parameter can be set multiple time.

Regards,

--
Julien Grall

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