On Sat, 2021-08-21 at 19:20 +0000, Edgecombe, Rick P wrote:

+KVM list.

On Fri, 2021-08-20 at 11:11 -0700, Yu-cheng Yu wrote:

quoted

 
 static inline int pte_write(pte_t pte)
 {
-       return pte_flags(pte) & _PAGE_RW;
+       /*
+        * Shadow stack pages are always writable - but not by
normal
+        * instructions, and only by shadow stack operations. 
Therefore,
+        * the W=0,D=1 test with pte_shstk().
+        */
+       return (pte_flags(pte) & _PAGE_RW) || pte_shstk(pte);
 }
 

KVM uses this in a couple places when checking EPT ptes. But bit 6
(dirty) is a totally different meaning in EPT. I think it's just used
to trigger an optimization, but wondering if KVM should have its own
TDP specific function instead of using pte_write().

Argh, never mind. I misread the new KVM mmu notifier refactor.