diff options
Diffstat (limited to 'arch/x86/kernel/alternative.c')
| -rw-r--r-- | arch/x86/kernel/alternative.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 133b549dc091..76ad4ce454c0 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -28,6 +28,7 @@ #include <asm/insn.h> #include <asm/io.h> #include <asm/fixmap.h> +#include <asm/paravirt.h> int __read_mostly alternatives_patched; @@ -733,6 +734,33 @@ void __init alternative_instructions(void) * patching. */ + /* + * Paravirt patching and alternative patching can be combined to + * replace a function call with a short direct code sequence (e.g. + * by setting a constant return value instead of doing that in an + * external function). + * In order to make this work the following sequence is required: + * 1. set (artificial) features depending on used paravirt + * functions which can later influence alternative patching + * 2. apply paravirt patching (generally replacing an indirect + * function call with a direct one) + * 3. apply alternative patching (e.g. replacing a direct function + * call with a custom code sequence) + * Doing paravirt patching after alternative patching would clobber + * the optimization of the custom code with a function call again. + */ + paravirt_set_cap(); + + /* + * First patch paravirt functions, such that we overwrite the indirect + * call with the direct call. + */ + apply_paravirt(__parainstructions, __parainstructions_end); + + /* + * Then patch alternatives, such that those paravirt calls that are in + * alternatives can be overwritten by their immediate fragments. + */ apply_alternatives(__alt_instructions, __alt_instructions_end); #ifdef CONFIG_SMP @@ -751,8 +779,6 @@ void __init alternative_instructions(void) } #endif - apply_paravirt(__parainstructions, __parainstructions_end); - restart_nmi(); alternatives_patched = 1; } |