On Thu, 2024-12-12 at 11:02 +0800, Baoquan He wrote: > Hi David, > > On 12/09/24 at 02:07pm, David Woodhouse wrote: > > In https://git.kernel.org/torvalds/c/07fa619f2a40c there is a test > > program which uses kexec to invoke a 4-instruction 'executable' which > > merely writes a byte to a serial port and returns. > > > > It just loads a single kexec segment containing those four > > instructions. > > > > Should I have been able to do that using kexec-tools? I couldn't work > > out how. > > > > And even once it's loaded, 'kexec -f -e' does manage to invoke it, but > > then reports 'No such file or directory' after the reboot() system call > > returns success. Strace shows: > > May I know why you are testing preserve-context feature recently? I > noticed you have raised an issue inside kernel and worked out a draft > patch, while you did't tell what use case or scenario preserve-context > is used in. Asking this because you could be the 1st one to test it and > report issues on preserve-context as far as I know these years. Right now, I'm testing it because I touched that code path in relocate_kernel_64.S and thus of *course* I have to test it. How could anyone touch this code and *not* test for regressions? > If there's newly found scenario preserve-context is needed, that's a > good thing. Otherwise we may consider to put it in DEPRECATED list in > kernel config so that we can finally take it off from kernel in several > years, like this people won't meet it and need take time to study what > it is and why it doesn't work as it was declared. What do you think? By coincidence, however, I do happen to know of a production scenario in which preserve-context kexec is used a few million times a week. (Which is lucky, because I was able to crib some of my test case from that code base.) The reload-GDT fix is also already in that code base, FWIW, and I have already frowned at them for not upstreaming it immediately, which was a violation of our development policy.
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