x86/mm: Rework wbinvd, hlt operation in stop_this_cpu()

Some issues have been reported with the for loop in stop_this_cpu() that
issues the 'wbinvd; hlt' sequence.  Reverting this sequence to halt()
has been shown to resolve the issue.

However, the wbinvd is needed when running with SME.  The reason for the
wbinvd is to prevent cache flush races between encrypted and non-encrypted
entries that have the same physical address.  This can occur when
kexec'ing from memory encryption active to inactive or vice-versa.  The
important thing is to not have outside of kernel text memory references
(such as stack usage), so the usage of the native_*() functions is needed
since these expand as inline asm sequences.  So instead of reverting the
change, rework the sequence.

Move the wbinvd instruction outside of the for loop as native_wbinvd()
and make its execution conditional on X86_FEATURE_SME.  In the for loop,
change the asm 'wbinvd; hlt' sequence back to a halt sequence but use
the native_halt() call.

Fixes: bba4ed011a52 ("x86/mm, kexec: Allow kexec to be used with SME")
Reported-by: Dave Young <[email protected]>
Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Dave Young <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Yu Chen <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Borislav Petkov <[email protected]>
Cc: Rui Zhang <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]

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