Messages in this thread | | | Subject | Re: [PATCH 17/24] x86/entry: Introduce struct ist_regs | From | Lai Jiangshan <> | Date | Fri, 10 Sep 2021 08:36:46 +0800 |
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On 2021/9/10 08:18, Lai Jiangshan wrote: > > > On 2021/9/1 01:50, Lai Jiangshan wrote: >> From: Lai Jiangshan <laijs@linux.alibaba.com> >> >> struct ist_regs is the upmost stack frame for IST interrupt, it >> consists of struct pt_regs and other fields which will be added in >> later patch. >> >> Make vc_switch_off_ist() take ist_regs as its argument and it will switch >> the whole ist_regs if needed. >> >> Make the frame before calling paranoid_entry() and paranoid_exit() be >> struct ist_regs. >> >> This patch is prepared for converting paranoid_entry() and paranoid_exit() >> into C code which will need the additinal fields to store the results in >> paranoid_entry() and to use them in paranoid_exit(). > > This patch was over designed. > > In ASM code, we can easily save results in the callee-saved registers. > For example, rc3 is saved in %r14, gsbase info is saved in %rbx. > > And in C code, we can't save results in registers. And I thought there was > no place to save the results because the CR3 and gsbase are not kernel's. > So I extended the pt_regs to ist_regs to save the results. > > But it was incorrect. The results can be saved in percpu data at the end of > paranoid_entry() after the CR3/gsbase are settled down. And the results > can be read at the beginning of paranoid_exit() before the CR3/gsbase are > switched to the interrupted context's. > > sigh.
Sigh again. IST interrupts can be nested. We can't save the results in percpu data unless we make it stack-like which is not a good idea. The changelog failed to express it.
> >> >> The C interrupt handlers don't use struct ist_regs due to they don't need >> the additional fields in the struct ist_regs, and they still use pt_regs. >> >
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