Re: [PATCH v5 07/14] nEPT: Add EPT tables support to paging_tmpl.h

Xiao Guangrong
2013-08-01T07:31:09Z

On 08/01/2013 03:18 PM, Xiao Guangrong wrote:
+#endif
>>>
>>> Hmm, why not use shadow_x_mask, shadow_user_mask instead? PT_WRITABLE_MASK
>>> is also suitable for ept, i guess we can remove the "#if/#else/#endif" after
>>> that.
>>>
>> shadow_x_mask and shadow_user_mask do not depend on guest paging mode,
>> so cannot be used here. Since we have to use ifdefs anyway relying on
>> VMX_EPT_WRITABLE_MASK == PT_WRITABLE_MASK is not necessary. Makes code
>> easier to read.
>
> Oh, yes, you are right.
>
> Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>

BTW, i notice the code in mmu.c uses PT64_NX_MASK to check the permission,
i.e:

static bool need_remote_flush(u64 old, u64 new)
{
if (!is_shadow_present_pte(old))
return false;
if (!is_shadow_present_pte(new))
return true;
if ((old ^ new) & PT64_BASE_ADDR_MASK)
return true;
old ^= PT64_NX_MASK;
new ^= PT64_NX_MASK;
return (old & ~new & PT64_PERM_MASK) != 0;
}

It checks shadow page table and the mask is wrong one nest ept spte.