Hi Christoffer, On 31/01/2019 08:04, Christoffer Dall wrote: > On Thu, Jan 24, 2019 at 04:32:56PM +0000, James Morse wrote: >> The hyp-stub is loaded by the kernel's early startup code at EL2 >> during boot, before KVM takes ownership later. The hyp-stub's >> text is part of the regular kernel text, meaning it can be kprobed. >> >> A breakpoint in the hyp-stub causes the CPU to spin in el2_sync_invalid. >> >> Add it to the __hyp_text. >> This has been a problem since kprobes was merged, it should >> probably have been covered in 888b3c8720e0. >> >> I'm not sure __hyp_text is the right place. Its not idmaped, >> and as it contains a set of vectors, adding it to the host/hyp >> idmap sections could grow them beyond a page... but it does >> run with the MMU off, so does need to be cleaned to PoC when >> anything wacky, like hibernate happens. With this patch, >> hibernate should clean the __hyp_text to PoC too. > > How did this code get cleaned before? It didn't need to be cleaned as KVM executes it with the MMU on. KVM's MMU-off code lives in the hyp_idmap, which is cleaned. (as is the kernel's idmap). The hibernate-cache-cleaning was trying to do the absolute minimum, but the hyp-stub got forgotten. > Is there a problem you can identify with putting it in __hyp_text? > Seems to me we should just stick it there if it has no negative > side-effects and otherwise we have to make up a separate section with a > specialized meaning. Yup, there is no problem with the extra cache-maintenance. The hyp-stub is the odd one out, its runtime code that runs with the MMU off, but isn't idmaped. I wasn't sure if we wanted to create some special section.(having to name it is a good enough reason not to!) Thanks, James _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
