On Mon, 2018-08-27 at 19:10 -0700, Andy Lutomirski wrote:
On Mon, Aug 27, 2018 at 6:31 PM, Rik van Riel riel@surriel.com wrote:
What is special about this path wrt nmi_uaccess_ok that is not also true for the need_flush branch right above it?
What am I missing?
Nothing. My patch is buggy. ETOLITTLESLEEP.
I could drop this part of the patch entirely. Or I could drop the loaded_mm->pgd == __va(read_cr3_pa() check and instead make sure that loaded_mm is NULL at any point at which loaded_mm might not match CR3. The latter will be faster in any (hypothetical) virtualization environment where CR3 reads trap. I don't know if we have any such cases where perf works and we care about performance, though.
Moving that loaded_mm = NULL assignment up a few lines, so it comes before the "if (need_flush)" test and covers both branches should cover that, indeed.