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Date: Wed, 6 Feb 2019 15:29:59 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
"Steven Rostedt (VMware)" <rostedt@...dmis.org>,
Jiri Kosina <jkosina@...e.cz>,
Josh Poimboeuf <jpoimboe@...hat.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Chris von Recklinghausen <crecklin@...hat.com>,
Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V4 9/9] x86/jump_label: Batch jump label updates
Hi Daniel,
On Mon, 4 Feb 2019 20:59:02 +0100
Daniel Bristot de Oliveira <bristot@...hat.com> 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@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
> Cc: Chris von Recklinghausen <crecklin@...hat.com>
> Cc: Jason Baron <jbaron@...mai.com>
> Cc: Scott Wood <swood@...hat.com>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> Cc: Clark Williams <williams@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> ---
> 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@...nel.org>
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