On 1/25/2021 1:55 PM, Borislav Petkov wrote:
On Mon, Jan 25, 2021 at 01:27:51PM -0800, Yu, Yu-cheng wrote:
Maybe I'm missing something but those two can happen outside of the
loop, no? Or is *ptep somehow changing concurrently while the loop is
doing the CMPXCHG and you need to recreate it each time?
IOW, you can generate upfront and do the empty loop...
*ptep can change concurrently.
Care to elaborate?
For example, when a thread reads a W=1, D=0 PTE and before changing it
to W=0,D=0, another thread could have written to the page and the PTE is
W=1, D=1 now. When try_cmpxchg() detects the difference, old_pte is
read again.
