Messages in this thread | | | Subject | Re: [PATCH 17/24] x86/entry: Introduce struct ist_regs | From | Lai Jiangshan <> | Date | Fri, 10 Sep 2021 08:18:47 +0800 |
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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.
> > 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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