[PATCH v3] KVM: arm64: Use BTI for nvhe

[Linux regression tracking (Thorsten Leemhuis)]

[CCing the regression list, as it should be in the loop for regressions:
https://docs.kernel.org/admin-guide/reporting-regressions.html]

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
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On 04.07.23 15:41, Sudeep Holla wrote:
> On Tue, May 30, 2023 at 03:08:45PM +0000, Mostafa Saleh wrote:
>> CONFIG_ARM64_BTI_KERNEL compiles the kernel to support ARMv8.5-BTI.
>> However, the nvhe code doesn't make use of it as it doesn't map any
>> pages with Guarded Page(GP) bit.
> [...]
> I was chasing a bug in linux-next yesterday with protected nVHE(pKVM) and
> cpuidle enabled. The system fails to boot. I just bisected the issue to this
> patch and also saw this patch landed in the linus tree yesterday/today.
> Not sure if this is something to do with the fact that pKVM skips to
> __kvm_handle_stub_hvc in __host_hvc.
> 
> Let me know if you want be to try something.

Thanks for the report. Seems the fix is slow to progress. Hence to be
sure the issue doesn't fall through the cracks unnoticed, I'm adding it
to regzbot, the Linux kernel regression tracking bot:

#regzbot ^introduced b53d4a272349
#regzbot title KVM: arm64: boot failures due to missing bti instructions
#regzbot monitor:
https://lore.kernel.org/all/20230706152240.685684-1-smostafa@google.com/
#regzbot fix: KVM: arm64: Add missing BTI instructions
#regzbot ignore-activity

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
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