Re: [PATCH V4 9/9] x86/jump_label: Batch jump label updates

[Masami Hiramatsu]

Hi Daniel,

On Mon,  4 Feb 2019 20:59:02 +0100
Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:

> Currently, the jump label of a static key is transformed via the arch
> specific function:
> 
>     void arch_jump_label_transform(struct jump_entry *entry,
>                                    enum jump_label_type type)
> 
> The new approach (batch mode) uses two arch functions, the first has the
> same arguments of the arch_jump_label_transform(), and is the function:
> 
>     void arch_jump_label_transform_queue(struct jump_entry *entry,
> 					 enum jump_label_type type)

This function actually returns "int" value.
Also, it seems the function returns 0 for failure and 1 for success,
but usually we guess "int" returns -errno or 0 for success.

So could you update the inferface to return -ENOSPC for vector
overflow, and -EINVAL for invalid entry?

Thank you,

> 
> Rather than transforming the code, it adds the jump_entry in a queue of
> entries to be updated. This functions returns 1 in the case of a
> successful enqueue of an entry. If it returns 0, the caller must to
> apply the queue and then try to queue again, for instance, because the
> queue is full.
> 
> This function expects the caller to sort the entries by the address before
> enqueueuing then. This is already done by the arch independent code, though.
> 
> After queuing all jump_entries, the function:
> 
>     void arch_jump_label_transform_apply(void)
> 
> Applies the changes in the queue.
> 
> Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> Cc: Jiri Kosina <jkosina@xxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
> Cc: Chris von Recklinghausen <crecklin@xxxxxxxxxx>
> Cc: Jason Baron <jbaron@xxxxxxxxxx>
> Cc: Scott Wood <swood@xxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> Cc: Clark Williams <williams@xxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  arch/x86/include/asm/jump_label.h |  2 +
>  arch/x86/kernel/jump_label.c      | 88 +++++++++++++++++++++++++++++++
>  2 files changed, 90 insertions(+)
> 
> diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
> index 65191ce8e1cf..06c3cc22a058 100644
> --- a/arch/x86/include/asm/jump_label.h
> +++ b/arch/x86/include/asm/jump_label.h
> @@ -2,6 +2,8 @@
>  #ifndef _ASM_X86_JUMP_LABEL_H
>  #define _ASM_X86_JUMP_LABEL_H
>  
> +#define HAVE_JUMP_LABEL_BATCH
> +
>  #define JUMP_LABEL_NOP_SIZE 5
>  
>  #ifdef CONFIG_X86_64
> diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
> index 2ef687db5a87..3c81cf8f06ca 100644
> --- a/arch/x86/kernel/jump_label.c
> +++ b/arch/x86/kernel/jump_label.c
> @@ -15,6 +15,7 @@
>  #include <asm/kprobes.h>
>  #include <asm/alternative.h>
>  #include <asm/text-patching.h>
> +#include <linux/slab.h>
>  
>  union jump_code_union {
>  	char code[JUMP_LABEL_NOP_SIZE];
> @@ -130,6 +131,93 @@ void arch_jump_label_transform(struct jump_entry *entry,
>  	mutex_unlock(&text_mutex);
>  }
>  
> +struct text_to_poke *entry_vector;
> +unsigned int entry_vector_max_elem __read_mostly;
> +unsigned int entry_vector_nr_elem;
> +
> +void arch_jump_label_init(void)
> +{
> +	entry_vector = (void *) __get_free_page(GFP_KERNEL);
> +
> +	if (WARN_ON_ONCE(!entry_vector))
> +		return;
> +
> +	entry_vector_max_elem = PAGE_SIZE / sizeof(struct text_to_poke);
> +	return;
> +}
> +
> +int arch_jump_label_transform_queue(struct jump_entry *entry,
> +				     enum jump_label_type type)
> +{
> +	void *entry_code;
> +	struct text_to_poke *tp;
> +
> +	/*
> +	 * Batch mode disabled before being able to allocate memory:
> +	 * Fallback to the non-batching mode.
> +	 */
> +	if (unlikely(!entry_vector_max_elem)) {
> +		if (!slab_is_available() || early_boot_irqs_disabled)
> +			goto fallback;
> +
> +		arch_jump_label_init();
> +	}
> +
> +	/*
> +	 * No more space in the vector, tell upper layer to apply
> +	 * the queue before continuing.
> +	 */
> +	if (entry_vector_nr_elem == entry_vector_max_elem)
> +		return 0;
> +
> +	tp = &entry_vector[entry_vector_nr_elem];
> +
> +	entry_code = (void *)jump_entry_code(entry);
> +
> +	/*
> +	 * The int3 handler will do a bsearch in the queue, so we need entries
> +	 * to be sorted. We can survive an unsorted list by rejecting the entry,
> +	 * forcing the generic jump_label code to apply the queue. Warning once,
> +	 * to raise the attention to the case of an unsorted entry that is
> +	 * better not happen, because, in the worst case we will perform in the
> +	 * same way as we do without batching - with some more overhead.
> +	 */
> +	if (entry_vector_nr_elem > 0) {
> +		int prev_idx = entry_vector_nr_elem - 1;
> +		struct text_to_poke *prev_tp = &entry_vector[prev_idx];
> +
> +		if (WARN_ON_ONCE(prev_tp->addr > entry_code))
> +			return 0;
> +	}
> +
> +	__jump_label_set_jump_code(entry, type,
> +				   (union jump_code_union *) &tp->opcode, 0);
> +
> +	tp->addr = entry_code;
> +	tp->handler = entry_code + JUMP_LABEL_NOP_SIZE;
> +	tp->len = JUMP_LABEL_NOP_SIZE;
> +
> +	entry_vector_nr_elem++;
> +
> +	return 1;
> +
> +fallback:
> +	arch_jump_label_transform(entry, type);
> +	return 1;
> +}
> +
> +void arch_jump_label_transform_apply(void)
> +{
> +	if (early_boot_irqs_disabled || !entry_vector_nr_elem)
> +		return;
> +
> +	mutex_lock(&text_mutex);
> +	text_poke_bp_batch(entry_vector, entry_vector_nr_elem);
> +	mutex_unlock(&text_mutex);
> +
> +	entry_vector_nr_elem = 0;
> +}
> +
>  static enum {
>  	JL_STATE_START,
>  	JL_STATE_NO_UPDATE,
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>