linux-kernel - Re: [PATCH v2 03/13] uprobes: allow arch access to xol slot

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Message-ID: <20131029154006.GA22344@redhat.com>
Date:	Tue, 29 Oct 2013 16:40:06 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Long <dave.long@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, Rabin Vincent <rabin@....in>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/13] uprobes: allow arch access to xol slot

On 10/22, David Long wrote:
>
> On 10/19/13 12:36, Oleg Nesterov wrote:
>>
>> How about
>>
>> 	void __weak arch_uprobe_xol_copy(...)
>> 	{
>> 		copy_to_page(...);
>> 	}
>>
>> then just
>>
>> 	- copy_to_page(...);
>> 	+ arch_uprobe_xol_copy(...);
>>
>> ?
>>
>
> I was trying to avoid duplicating the VM calls in the
> architecture-specific implementations,

Yes, I understand... But this uglifies the generic code.

> but maybe that is the cleaner way
> to do it after all.  I've made changes as suggested above.

Thanks. and this uglifies arm code I guess ;)


David. Perhaps we can avoid the new hook altogether? What if we do
the simple change below (it ignores powerpc) ?

Then arm can add "unsigned long ixol[2]" into its arch_uprobe, and
arch_uprobe_analyze_insn() can initialize this member correctly.

What do you think?

Oleg.

--- x/arch/x86/include/asm/uprobes.h
+++ x/arch/x86/include/asm/uprobes.h
@@ -35,7 +35,10 @@ typedef u8 uprobe_opcode_t;
 
 struct arch_uprobe {
 	u16				fixups;
-	u8				insn[MAX_UINSN_BYTES];
+	union {
+		u8			insn[MAX_UINSN_BYTES];
+		u8			ixol[MAX_UINSN_BYTES];
+	}
 #ifdef CONFIG_X86_64
 	unsigned long			rip_rela_target_address;
 #endif
--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -1264,7 +1264,8 @@ static unsigned long xol_get_insn_slot(s
 		return 0;
 
 	/* Initialize the slot */
-	copy_to_page(area->page, xol_vaddr, uprobe->arch.insn, MAX_UINSN_BYTES);
+	copy_to_page(area->page, xol_vaddr,
+			uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
 	/*
 	 * We probably need flush_icache_user_range() but it needs vma.
 	 * This should work on supported architectures too.

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