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Re: [Xen-devel] [PATCH] x86/EPT: defer enabling of A/D maintenance until PML get enabled





On 10/15/2015 03:35 PM, Kai Huang wrote:


On 10/15/2015 03:11 PM, Jan Beulich wrote:
On 15.10.15 at 08:42, <kai.huang@xxxxxxxxxxxxxxx> wrote:
Thanks for your comments Jan. Actually I am not happy with combining
with EPT A/D bit update with PML enabling to single function. After
thinking again, how about adding a separate vmx function (ex,
vmx_domain_update_eptp) to update EPTP of VMCS of all vcpus of domain
after p2m->ept.ept_ad is updated. Another good is this function can also
be used in the future for other runtime updates to p2m->ept.

What's your idea?
I don't mind, but that's really more of a question to the VMX maintainers.
Then I would prefer this way.

Kevin,

Do you have any comments on this thread?

--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -1129,17 +1129,26 @@ void ept_sync_domain(struct p2m_domain *p2m)

   static void ept_enable_pml(struct p2m_domain *p2m)
   {
       /*
- * No need to check if vmx_domain_enable_pml has succeeded or not, as + * No need to return if vmx_domain_enable_pml has succeeded or not, as
It seems to me that you'd better use "whether" instead of "if" now
(and then perhaps also drop the "or not").
OK. Thanks.

* ept_p2m_type_to_flags will do the check, and write protection will be
        * used if PML is not enabled.
        */
-    vmx_domain_enable_pml(p2m->domain);
+    if ( vmx_domain_enable_pml(p2m->domain) )
+        return;
+
+    p2m->ept.ept_ad = 1;
+    vmx_domain_update_eptp(p2m->domain);
Shouldn't you enable A/D _before_ enabling PML, at least without
having a domain-is-paused check here?
Looks we don't have such function. How about just add ASSERT(atomic_read(&d->pause_count)), just the same as in vmx_domain_enable_pml ?
I mean we can enable A/D before enabling PML, but if so we need additional code to clear A/D bit if vmx_domain_enable_pml failed. My thinking is considering the function is called when domain is paused, so there's no difference to enable A/D before or after enabling PML.

Thanks,
-Kai

Thanks,
-Kai

Jan




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