On 23/06/20 10:27, Vitaly Kuznetsov wrote:
> 'nmi_hlt' test returns somewhat weird result:
>
> ...
> PASS: direct NMI + hlt
> PASS: NMI intercept while running guest
> PASS: intercepted NMI + hlt
> PASS: nmi_hlt
> SUMMARY: 4 tests, 1 unexpected failures
>
> Trying to investigate where the failure is coming from I was tweaking
> the code around and with tiny meaningless changes I was able to observe
> #PF, #GP, #UD and other 'interesting' results. Compiler optimization
> flags also change the outcome so there's obviously a corruption somewhere.
> Adding a meaningless 'nop' to the second 'asm volatile ("hlt");' in
> nmi_hlt_test() saves the day so it seems we erroneously advance RIP
> twice, the advancement in nmi_hlt_finished() is not needed.
>
> The outcome, however, contradicts with the commit message in 7e7aa86f74
> ("SVM: move guest past HLT"). With that commit reverted, all tests seem
> to pass but I'm not sure what issue the commit was trying to fix, thus
> RFC.
>
> This reverts commit 7e7aa86f7418a8343de46583977f631e55fd02ed.
Hmm it's possible that the commit was working around something bad in
nested SVM in the middle of the development. I cannot see the
unexpected failure, but reverting the patch does not seem to have any
ill effect. I pushed the patch, thanks.
Paolo
