Messages in this thread | | | Date | Thu, 22 Jul 2021 08:19:30 -0700 | From | "Luck, Tony" <> | Subject | Re: [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery |
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On Thu, Jul 22, 2021 at 06:54:37AM -0700, Jue Wang wrote: > This patch assumes the UC error consumed in kernel is always the same UC. > > Yet it's possible two UCs on different pages are consumed in a row. > The patch below will panic on the 2nd MCE. How can we make the code works > on multiple UC errors? > > > > + int count = ++current->mce_count; > > + > > + /* First call, save all the details */ > > + if (count == 1) { > > + current->mce_addr = m->addr; > > + current->mce_kflags = m->kflags; > > + current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); > > + current->mce_whole_page = whole_page(m); > > + current->mce_kill_me.func = func; > > + } > > ...... > > + /* Second or later call, make sure page address matches the one from first call */ > > + if (count > 1 && (current->mce_addr >> PAGE_SHIFT) != (m->addr >> PAGE_SHIFT)) > > + mce_panic("Machine checks to different user pages", m, msg);
The issue is getting the information about the location of the error from the machine check handler to the "task_work" function that processes it. Currently there is a single place to store the address of the error in the task structure:
current->mce_addr = m->addr;
Plausibly that could be made into an array, indexed by current->mce_count to save mutiple addresses (perhaps also need mce_kflags, mce_ripv, etc. to also be arrays).
But I don't want to pre-emptively make such a change without some data to show that situations arise with multiple errors to different addresses: 1) Actually occur 2) Would be recovered if we made the change.
The first would be indicated by seeing the:
"Machine checks to different user pages"
panic. You'd have to code up the change to have arrays to confirm that would fix the problem.
-Tony
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