Chen, Kenneth W wrote:
A more favorable change is to remove comparing pud/pmd entry, but condition the vhpt TLB purging upon detecting pte modification. I had this patch in my pocket for a while for other optimizations I'm working on and it looks like a good timing to post it now.
I cannot agree with you. 1. If *pte becomes invalid in the mean time, then the translation for the PTE page can be still valid. E.g. the swapper removes PTE-s and purges the translations for user pages only, never for a PTE page. 2. Let's have a look at your posting on the 30th os March, in the thread "accessed/dirty bit handler tuning":
cpu0 cpu1 cpu2
Vhpt miss:
walk page table
free_pgtables
ptc.g fault address
ptc.g hash address
pud_alloc/pmd_alloc
new page instantiation
itc.d faulting address
itc.d hash address
read pte
kill tlb for fault addr
rfi
Touch fault addr
Walker install the tlb
with staled vhpt tlb
-> using someone else's page
-> data corruption
I did agree with you. In addition, I wanted to add a protection for protecting the pgd ... pte chain walking. I wanted to use the mm semaphore => no need to walk again the pgd ... pte chain. I think your new patch widens the security hole. Regards, Zoltan - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|