linux-kernel - Re: [PATCH 0/1] (Was: Linux 3.11-rc4)

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Date:	Thu, 8 Aug 2013 20:15:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Grazvydas Ignotas <notasas@...il.com>,
	Felipe Contreras <felipe.contreras@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH 0/1] (Was: Linux 3.11-rc4)

On 08/08, Frederic Weisbecker wrote:
>
> I'm all for fixing this. May be we can start by backporting a patch that
> ignores the value of gen_len for instruction breakpoints in x86?

Or perhaps we can start with the something like below.

But probably we should move "attr.bp_len == HW_BREAKPOINT_LEN_1" check
from arch_build_bp_info() to its caller, arch_validate_hwbkpt_settings().

Because:

> But this bp_len
> should rather be used for range breakpoints on archs that support it.

Yes, exactly, and we already have the patches for amd, so bp->len can
be actually != 1 but currently we can't support because it is checked
in arch_build_bp_info().

Oleg.

--- x/arch/x86/kernel/hw_breakpoint.c
+++ x/arch/x86/kernel/hw_breakpoint.c
@@ -208,19 +208,16 @@ int arch_bp_generic_fields(int x86_len, 
 {
 	/* Type */
 	switch (x86_type) {
-	case X86_BREAKPOINT_EXECUTE:
-		if (x86_len != X86_BREAKPOINT_LEN_X)
-			return -EINVAL;
-
-		*gen_type = HW_BREAKPOINT_X;
-		*gen_len = sizeof(long);
-		return 0;
 	case X86_BREAKPOINT_WRITE:
 		*gen_type = HW_BREAKPOINT_W;
 		break;
 	case X86_BREAKPOINT_RW:
 		*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
 		break;
+	case X86_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		if (x86_len == X86_BREAKPOINT_LEN_1)
+			break;
 	default:
 		return -EINVAL;
 	}
@@ -265,15 +262,11 @@ static int arch_build_bp_info(struct per
 		break;
 	case HW_BREAKPOINT_X:
 		info->type = X86_BREAKPOINT_EXECUTE;
-		/*
-		 * x86 inst breakpoints need to have a specific undefined len.
-		 * But we still need to check userspace is not trying to setup
-		 * an unsupported length, to get a range breakpoint for example.
-		 */
-		if (bp->attr.bp_len == sizeof(long)) {
-			info->len = X86_BREAKPOINT_LEN_X;
-			return 0;
-		}
+		/* until we change tools/perf */
+		if (bp->attr.bp_len == sizeof(long))
+			bp->attr.bp_len = HW_BREAKPOINT_LEN_1;
+		if (bp->attr.bp_len == HW_BREAKPOINT_LEN_1)
+			break;
 	default:
 		return -EINVAL;
 	}

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