Messages in this thread | | | From | Jue Wang <> | Date | Thu, 22 Jul 2021 16:30:44 -0700 | Subject | Re: [PATCH 2/3] x86/mce: Avoid infinite loop for copy from user recovery |
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I think the challenge being the uncorrectable errors are essentially random. It's just a matter of time for >1 UC errors to show up in sequential kernel accesses.
It's easy to create such cases with artificial error injections.
I suspect we want to design this part of the kernel to be able to handle generic cases?
Thanks, -Jue
On Thu, Jul 22, 2021 at 8:19 AM Luck, Tony <tony.luck@intel.com> wrote: > > 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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