Re: [PATCH v2 12/13] KVM: x86: add SMM to the MMU role, support SMRAM address space

From: Xiao Guangrong
Date: Thu Jun 18 2015 - 01:07:06 EST

On 06/17/2015 04:18 PM, Paolo Bonzini wrote:

On 09/06/2015 06:01, Xiao Guangrong wrote:

On 05/28/2015 01:05 AM, Paolo Bonzini wrote:
This is now very simple to do. The only interesting part is a simple
trick to find the right memslot in gfn_to_rmap, retrieving the address
space from the spte role word. The same trick is used in the auditing

The comment on top of union kvm_mmu_page_role has been stale forever,

Fortunately, we have documented these fields in mmu.txt, please do it for
'smm' as well. :)

Right, done.

+ /*
+ * This is left at the top of the word so that
+ * kvm_memslots_for_spte_role can extract it with a
+ * simple shift. While there is room, give it a whole
+ * byte so it is also faster to load it from memory.
+ */
+ unsigned smm:8;

I suspect if we really need this trick, smm is not the hottest filed in
this struct anyway.

Note that after these patches it is used by gfn_to_rmap, and hence for
example rmap_add.

However, role->level is more hotter than role->smm so that it's also a good
candidate for this kind of trick.

And this is only 32 bits which can be operated in a CPU register by a single
memory load, that is why i was worried if it is really needed.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at