Re: [PATCH 01/10] VMX: Enable EPT A/D bit support

From: Tim Deegan <tim@xen.org>
To: Kai Huang <kai.huang@linux.intel.com>
Cc: yang.z.zhang@intel.com, andrew.cooper3@citrix.com,
	kevin.tian@intel.com, jbeulich@suse.com, xen-devel@lists.xen.org
Subject: Re: [PATCH 01/10] VMX: Enable EPT A/D bit support
Date: Thu, 9 Apr 2015 12:21:25 +0100	[thread overview]
Message-ID: <20150409112125.GE17031@deinos.phlegethon.org> (raw)
In-Reply-To: <1427423754-11841-2-git-send-email-kai.huang@linux.intel.com>

At 10:35 +0800 on 27 Mar (1427452545), Kai Huang wrote:
> @@ -233,6 +233,9 @@ static int ept_split_super_page(struct p2m_domain *p2m, ept_entry_t *ept_entry,
>      if ( !ept_set_middle_entry(p2m, &new_ept) )
>          return 0;
>  
> +    /* It's better to copy A bit of Middle entry from original entry */
> +    new_ept.a = ept_entry->a;

Shouldn't this A bit always be set to 1?  After all we're not using it
for anything, and it doesn't mean the same thing as the A bit in the
superpage entry did.

In fact, thinking about that, we should probably be setting _all_ the
A bits to 1, even in leaf entries, to avoid the overhead of the MMU
having to write them later.

Cheers,

Tim.