Re: [Xen-devel] [PATCH 2/5] xen/alternatives: Plumb a 'live' parameter through apply_alternatives()

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 29 Jan 2018, Andrew Cooper wrote:
> On x86, we would like to alter how we patch based on whether there is any
> chance of the code being patched being concurrently executed.
> 
> prepare_payload() passes false (as the livepatch definitely isn't live at this
> point), whereas the boot-time alternatives application passes true.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>  xen/arch/arm/alternative.c        | 10 ++++++----
>  xen/arch/x86/alternative.c        |  5 +++--
>  xen/common/livepatch.c            |  2 +-
>  xen/include/asm-arm/alternative.h |  6 ++++--
>  xen/include/asm-x86/alternative.h |  3 ++-
>  5 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c
> index 99112e1..078b259 100644
> --- a/xen/arch/arm/alternative.c
> +++ b/xen/arch/arm/alternative.c
> @@ -98,7 +98,8 @@ static u32 get_alt_insn(const struct alt_instr *alt,
>   * The region patched should be read-write to allow __apply_alternatives
>   * to replacing the instructions when necessary.
>   */
> -static void __apply_alternatives(const struct alt_region *region)
> +static void __apply_alternatives(const struct alt_region *region,
> +                                 bool live)
>  {
>      const struct alt_instr *alt;
>      const u32 *replptr;
> @@ -193,7 +194,7 @@ static int __init __apply_alternatives_multi_stop(void 
> *unused)
>          region.begin = (void *)__alt_instructions - (void *)_start + xenmap;
>          region.end = (void *)__alt_instructions_end - (void *)_start + 
> xenmap;
>  
> -        __apply_alternatives(&region);
> +        __apply_alternatives(&region, true);
>  
>          unregister_virtual_region(&patch_region);
>  
> @@ -224,14 +225,15 @@ void __init apply_alternatives_all(void)
>  }
>  
>  void apply_alternatives(const struct alt_instr *start,
> -                        const struct alt_instr *end)
> +                        const struct alt_instr *end,
> +                        bool live)
>  {
>      const struct alt_region region = {
>          .begin = start,
>          .end = end,
>      };
>  
> -    __apply_alternatives(&region);
> +    __apply_alternatives(&region, live);
>  }
>  
>  /*
> diff --git a/xen/arch/x86/alternative.c b/xen/arch/x86/alternative.c
> index ee18e6c..5b3fb80 100644
> --- a/xen/arch/x86/alternative.c
> +++ b/xen/arch/x86/alternative.c
> @@ -163,7 +163,8 @@ text_poke(void *addr, const void *opcode, size_t len)
>   * Tough. Make sure you disable such features by hand.
>   */
>  void init_or_livepatch apply_alternatives(const struct alt_instr *start,
> -                                          const struct alt_instr *end)
> +                                          const struct alt_instr *end,
> +                                          bool live)
>  {
>      const struct alt_instr *a;
>      u8 *instr, *replacement;
> @@ -235,7 +236,7 @@ void __init alternative_instructions(void)
>      /* Disable WP to allow application of alternatives to read-only pages. */
>      write_cr0(cr0 & ~X86_CR0_WP);
>  
> -    apply_alternatives(__alt_instructions, __alt_instructions_end);
> +    apply_alternatives(__alt_instructions, __alt_instructions_end, true);
>  
>      /* Reinstate WP. */
>      write_cr0(cr0);
> diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
> index b9376c9..6f03e89 100644
> --- a/xen/common/livepatch.c
> +++ b/xen/common/livepatch.c
> @@ -682,7 +682,7 @@ static int prepare_payload(struct payload *payload,
>                  return -EINVAL;
>              }
>          }
> -        apply_alternatives(start, end);
> +        apply_alternatives(start, end, false);
>  #else
>          dprintk(XENLOG_ERR, LIVEPATCH "%s: We don't support alternative 
> patching!\n",
>                  elf->name);
> diff --git a/xen/include/asm-arm/alternative.h 
> b/xen/include/asm-arm/alternative.h
> index 49a055e..77b0944 100644
> --- a/xen/include/asm-arm/alternative.h
> +++ b/xen/include/asm-arm/alternative.h
> @@ -26,7 +26,8 @@ struct alt_instr {
>  
>  void __init apply_alternatives_all(void);
>  void apply_alternatives(const struct alt_instr *start,
> -                        const struct alt_instr *end);
> +                        const struct alt_instr *end,
> +                        bool live);
>  
>  #define ALTINSTR_ENTRY(feature)                                              
>       \
>       " .word 661b - .\n"                             /* label           */ \
> @@ -160,7 +161,8 @@ static inline void apply_alternatives_all(void)
>  }
>  
>  static inline void apply_alternatives(const struct alt_instr *start,
> -                                      const struct alt_instr *end)
> +                                      const struct alt_instr *end,
> +                                      bool live)
>  {
>  }
>  
> diff --git a/xen/include/asm-x86/alternative.h 
> b/xen/include/asm-x86/alternative.h
> index ba537d6..07ff424 100644
> --- a/xen/include/asm-x86/alternative.h
> +++ b/xen/include/asm-x86/alternative.h
> @@ -23,7 +23,8 @@ struct alt_instr {
>  extern void add_nops(void *insns, unsigned int len);
>  /* Similar to alternative_instructions except it can be run with IRQs 
> enabled. */
>  extern void apply_alternatives(const struct alt_instr *start,
> -                               const struct alt_instr *end);
> +                               const struct alt_instr *end,
> +                               bool live);
>  extern void alternative_instructions(void);
>  
>  #define OLDINSTR(oldinstr)      "661:\n\t" oldinstr "\n662:\n"
> -- 
> 2.1.4
> 

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