x86/paravirt: Convert simple paravirt functions to asm

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

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 71bf64b963df..4acbcddddc29 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -559,8 +559,14 @@ void paravirt_flush_lazy_mmu(void);
 
 void _paravirt_nop(void);
 void paravirt_BUG(void);
-u64 _paravirt_ident_64(u64);
 unsigned long paravirt_ret0(void);
+#ifdef CONFIG_PARAVIRT_XXL
+u64 _paravirt_ident_64(u64);
+unsigned long pv_native_save_fl(void);
+void pv_native_irq_disable(void);
+void pv_native_irq_enable(void);
+unsigned long pv_native_read_cr2(void);
+#endif
 
 #define paravirt_nop	((void *)_paravirt_nop)