Linux Virtualization - Sep 2018 - [PATCH v2] x86/paravirt: Cleanup native_patch()

On Mon, Sep 10, 2018 at 08:54:12AM +0200, Juergen Gross
wrote:
> > +	case PARAVIRT_PATCH(lock.queued_spin_unlock):
> > +		if (pv_is_native_spin_unlock())
> > +			return paravirt_patch_insns(ibuf, len,
> > +						    start_lock_queued_spin_unlock,
> > +						    end_lock_queued_spin_unlock);
> > +		else
> > +			return paravirt_patch_default(type, ibuf, addr, len);
> 
> Why not replace the else clause by a "break;" and ...
Because I think that exiting right then and there is much easier to
follow than adding all those breaks and wading through ifdeffery
to realize that this is the default path and we'll end up calling
paravirt_patch_default() in the end.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

On 10/09/18 09:01, Borislav Petkov wrote:
> On Mon, Sep 10, 2018 at 08:54:12AM +0200, Juergen Gross wrote:
>>> +	case PARAVIRT_PATCH(lock.queued_spin_unlock):
>>> +		if (pv_is_native_spin_unlock())
>>> +			return paravirt_patch_insns(ibuf, len,
>>> +						    start_lock_queued_spin_unlock,
>>> +						    end_lock_queued_spin_unlock);
>>> +		else
>>> +			return paravirt_patch_default(type, ibuf, addr, len);
>>
>> Why not replace the else clause by a "break;" and ...
> 
> Because I think that exiting right then and there is much easier to
> follow than adding all those breaks and wading through ifdeffery
> to realize that this is the default path and we'll end up calling
> paravirt_patch_default() in the end.
> 
Really? All of the remaining coding would fit easily on one screen. No
hidden breaks anywhere and no deep nesting involved. And the ifdefs
hardly makes it more difficult to understand, as they are not even
nested.


Juergen

When CONFIG_PARAVIRT_SPINLOCKS=n, it fires

  arch/x86/kernel/paravirt_patch_64.c: In function ?native_patch?:
  arch/x86/kernel/paravirt_patch_64.c:89:1: warning: label ?patch_site? defined
but not used [-Wunused-label]
   patch_site:

but those labels can simply be removed by directly calling the
respective functions there.

Get rid of local variables too, while at it. Also, simplify function
flow for better readability.

Signed-off-by: Borislav Petkov <bp at suse.de>
Cc: Juergen Gross <jgross at suse.com>
Cc: x86 at kernel.org
Cc: virtualization at lists.linux-foundation.org
---

Here it is, rebased ontop of rc3+tip/master.


 arch/x86/kernel/paravirt_patch_32.c | 44 ++++++++++-----------------
 arch/x86/kernel/paravirt_patch_64.c | 46 +++++++++++------------------
 2 files changed, 33 insertions(+), 57 deletions(-)

diff --git a/arch/x86/kernel/paravirt_patch_32.c
b/arch/x86/kernel/paravirt_patch_32.c
index d460cbcabcfe..6368c22fa1fa 100644
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -34,14 +34,10 @@ extern bool pv_is_native_vcpu_is_preempted(void);
 
 unsigned native_patch(u8 type, void *ibuf, unsigned long addr, unsigned len)
 {
-	const unsigned char *start, *end;
-	unsigned ret;
-
 #define PATCH_SITE(ops, x)					\
-		case PARAVIRT_PATCH(ops.x):			\
-			start = start_##ops##_##x;		\
-			end = end_##ops##_##x;			\
-			goto patch_site
+	case PARAVIRT_PATCH(ops.x):				\
+		return paravirt_patch_insns(ibuf, len, start_##ops##_##x, end_##ops##_##x)
+
 	switch (type) {
 #ifdef CONFIG_PARAVIRT_XXL
 		PATCH_SITE(irq, irq_disable);
@@ -54,32 +50,24 @@ unsigned native_patch(u8 type, void *ibuf, unsigned long
addr, unsigned len)
 		PATCH_SITE(mmu, write_cr3);
 #endif
 #if defined(CONFIG_PARAVIRT_SPINLOCKS)
-		case PARAVIRT_PATCH(lock.queued_spin_unlock):
-			if (pv_is_native_spin_unlock()) {
-				start = start_lock_queued_spin_unlock;
-				end   = end_lock_queued_spin_unlock;
-				goto patch_site;
-			}
-			goto patch_default;
+	case PARAVIRT_PATCH(lock.queued_spin_unlock):
+		if (pv_is_native_spin_unlock())
+			return paravirt_patch_insns(ibuf, len,
+						    start_lock_queued_spin_unlock,
+						    end_lock_queued_spin_unlock);
+		break;
 
-		case PARAVIRT_PATCH(lock.vcpu_is_preempted):
-			if (pv_is_native_vcpu_is_preempted()) {
-				start = start_lock_vcpu_is_preempted;
-				end   = end_lock_vcpu_is_preempted;
-				goto patch_site;
-			}
-			goto patch_default;
+	case PARAVIRT_PATCH(lock.vcpu_is_preempted):
+		if (pv_is_native_vcpu_is_preempted())
+			return paravirt_patch_insns(ibuf, len,
+						    start_lock_vcpu_is_preempted,
+						    end_lock_vcpu_is_preempted);
+		break;
 #endif
 
 	default:
-patch_default: __maybe_unused
-		ret = paravirt_patch_default(type, ibuf, addr, len);
-		break;
-
-patch_site:
-		ret = paravirt_patch_insns(ibuf, len, start, end);
 		break;
 	}
 #undef PATCH_SITE
-	return ret;
+	return paravirt_patch_default(type, ibuf, addr, len);
 }
diff --git a/arch/x86/kernel/paravirt_patch_64.c
b/arch/x86/kernel/paravirt_patch_64.c
index 5ad5bcda9dc6..7ca9cb726f4d 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -42,15 +42,11 @@ extern bool pv_is_native_vcpu_is_preempted(void);
 
 unsigned native_patch(u8 type, void *ibuf, unsigned long addr, unsigned len)
 {
-	const unsigned char *start, *end;
-	unsigned ret;
-
 #define PATCH_SITE(ops, x)					\
-		case PARAVIRT_PATCH(ops.x):			\
-			start = start_##ops##_##x;		\
-			end = end_##ops##_##x;			\
-			goto patch_site
-	switch(type) {
+	case PARAVIRT_PATCH(ops.x):				\
+		return paravirt_patch_insns(ibuf, len, start_##ops##_##x, end_##ops##_##x)
+
+	switch (type) {
 #ifdef CONFIG_PARAVIRT_XXL
 		PATCH_SITE(irq, restore_fl);
 		PATCH_SITE(irq, save_fl);
@@ -64,32 +60,24 @@ unsigned native_patch(u8 type, void *ibuf, unsigned long
addr, unsigned len)
 		PATCH_SITE(mmu, write_cr3);
 #endif
 #if defined(CONFIG_PARAVIRT_SPINLOCKS)
-		case PARAVIRT_PATCH(lock.queued_spin_unlock):
-			if (pv_is_native_spin_unlock()) {
-				start = start_lock_queued_spin_unlock;
-				end   = end_lock_queued_spin_unlock;
-				goto patch_site;
-			}
-			goto patch_default;
+	case PARAVIRT_PATCH(lock.queued_spin_unlock):
+		if (pv_is_native_spin_unlock())
+			return paravirt_patch_insns(ibuf, len,
+						    start_lock_queued_spin_unlock,
+						    end_lock_queued_spin_unlock);
+		break;
 
-		case PARAVIRT_PATCH(lock.vcpu_is_preempted):
-			if (pv_is_native_vcpu_is_preempted()) {
-				start = start_lock_vcpu_is_preempted;
-				end   = end_lock_vcpu_is_preempted;
-				goto patch_site;
-			}
-			goto patch_default;
+	case PARAVIRT_PATCH(lock.vcpu_is_preempted):
+		if (pv_is_native_vcpu_is_preempted())
+			return paravirt_patch_insns(ibuf, len,
+						    start_lock_vcpu_is_preempted,
+						    end_lock_vcpu_is_preempted);
+		break;
 #endif
 
 	default:
-patch_default: __maybe_unused
-		ret = paravirt_patch_default(type, ibuf, addr, len);
-		break;
-
-patch_site:
-		ret = paravirt_patch_insns(ibuf, len, start, end);
 		break;
 	}
 #undef PATCH_SITE
-	return ret;
+	return paravirt_patch_default(type, ibuf, addr, len);
 }
-- 
2.17.0.582.gccdcbd54c

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.