x86/paravirt: Convert simple paravirt functions to asm

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All functions referenced via __PV_IS_CALLEE_SAVE() need to be assembler
functions, as those functions calls are hidden from the compiler.

In case the kernel is compiled with "-fzero-call-used-regs" the compiler
will clobber caller-saved registers at the end of C functions, which
will result in unexpectedly zeroed registers at the call site of the
related paravirt functions.

Replace the C functions with DEFINE_PARAVIRT_ASM() constructs using
the same instructions as the related paravirt calls in the
PVOP_ALT_[V]CALLEE*() macros. And since they're not C functions visible
to the compiler anymore, latter won't do the callee-clobbered zeroing
invoked by -fzero-call-used-regs and thus won't corrupt registers.

  [ bp: Extend commit message. ]

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230317063325.361-1-jgross@suse.com

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This commit is contained in:

Juergen Gross 2023-03-17 07:33:25 +01:00 • committed by Borislav Petkov (AMD)

parent c9ae1b10d9

commit 11af36cb89

2 changed files with 13 additions and 22 deletions

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8

arch/x86/include/asm/paravirt_types.h

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27

arch/x86/kernel/paravirt.c

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