x86/apic: Fix the issues in x2apic_disable()

PATCH Superseded Yuntao Wang 3 participants 6 messages Aug 12, 2024 – Aug 13, 2024

Subsystems (2)

Stable branch x86

lore

Share & tools

lore

Yuntao Wang

author

2024-08-12 10:09 UTC #0 lore raw

PATCH 1/1 x86/apic: Fix the issues in x2apic_disable()

There are two issues in x2apic_disable().

The first issue is that the 'pr_warn' in 'if (x2apic_hw_locked())' will never be executed, because when x2apic_hw_locked() evaluates to true, x2apic_state should be X2APIC_ON_LOCKED. However, the current logic in x2apic_disable() is that if x2apic_state is not X2APIC_ON, it returns early, so the subsequent logic will not be executed.

Therefore, 'if (state != X2APIC_ON)' should be changed to 'if (state < X2APIC_ON)', so that when x2apic_state is X2APIC_ON_LOCKED, the corresponding warning log can be printed.

The second issue is that the current logic of x2apic_disable() first sets x2apic_mode and x2apic_state to 0 and X2APIC_DISABLED, respectively, and then tries to disable x2APIC. However, when the APIC is locked in x2APIC mode, that is, x2apic_state is X2APIC_ON_LOCKED, x2APIC cannot be disabled, which causes the final values of the x2apic_mode/x2apic_state variables to be inconsistent with the actual state of x2APIC.

Let's fix these issues.

Signed-off-by Yuntao Wang <[email protected]>

---
 arch/x86/kernel/apic/apic.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

arch/x86/kernel/apic/apic.c +7 -6

index 66fd4b2a37a3..fce8d0214069 100644
@@ -1775,13 +1775,10 @@ static __init void apic_set_fixmap(bool read_apic);
 
 static __init void x2apic_disable(void)
 {
-	u32 x2apic_id, state = x2apic_state;
+	u32 x2apic_id;
 
-	x2apic_mode = 0;
-	x2apic_state = X2APIC_DISABLED;
-
-	if (state != X2APIC_ON)
-		return;
+	if (x2apic_state < X2APIC_ON)
+		goto out;
 
 	x2apic_id = read_apic_id();
 	if (x2apic_id >= 255)

@@ -1799,6 +1796,10 @@ static __init void x2apic_disable(void)
 	 * which fails to do the read after x2APIC was disabled.
 	 */
 	apic_set_fixmap(false);
+
+out:
+	x2apic_mode = 0;
+	x2apic_state = X2APIC_DISABLED;
 }
 
 static __init void x2apic_enable(void)

Signature · 1 line

2.46.0

Thomas Gleixner

2024-08-12 14:48 UTC #1 lore raw

arch/x86/kernel/apic/apic.c static __init void apic_set_fixmap(bool read_apic); · line 1781

Quoted 12 lines · Yuntao Wang

static __init void x2apic_disable(void)
{

arch/x86/kernel/apic/apic.c +3 -6

-	u32 x2apic_id, state = x2apic_state;
+	u32 x2apic_id;
 
-	x2apic_mode = 0;
-	x2apic_state = X2APIC_DISABLED;
-
-	if (state != X2APIC_ON)
-		return;
+	if (x2apic_state < X2APIC_ON)
+		goto out;

There is no point in overwriting the state in case it is < ON, no?

Thanks,

tglx

Yuntao Wang

author

2024-08-12 15:54 UTC #2 lore raw

Quoted 6 lines · Thomas Gleixner

Quoted 5 lines · Yuntao Wang
static __init void x2apic_disable(void)
{
arch/x86/kernel/apic/apic.c +1 -1
-	u32 x2apic_id, state = x2apic_state;
+	u32 x2apic_id;

Quoted 9 lines

arch/x86/kernel/apic/apic.c static __init void apic_set_fixmap(bool read_apic); · line 1781
Quoted 7 lines
arch/x86/kernel/apic/apic.c +2 -5
-	x2apic_mode = 0;
-	x2apic_state = X2APIC_DISABLED;
-
-	if (state != X2APIC_ON)
-		return;
+	if (x2apic_state < X2APIC_ON)
+		goto out;
There is no point in overwriting the state in case it is < ON, no?

Are you saying that we should replace 'goto out' with a return statement?

However, when x2apic_disable() is called, it's possible that x2apic_state is X2APIC_OFF. In that case, we should set x2apic_state to X2APIC_DISABLED.

So, I think overwriting the state is necessary.

Thanks,
Yuntao

Quoted 3 lines

Thanks,
tglx

Thomas Gleixner

2024-08-12 18:00 UTC #3 lore raw

Quoted 7 lines · Yuntao Wang

Quoted 1 line · Thomas Gleixner
There is no point in overwriting the state in case it is < ON, no?
Are you saying that we should replace 'goto out' with a return statement?
However, when x2apic_disable() is called, it's possible that x2apic_state is X2APIC_OFF. In that case, we should set x2apic_state to X2APIC_DISABLED.

What for? It can't be enabled later on and for the rest of the system it does not matter whether the state is OFF or DISABLED. Either case says:
X2APIC is not enabled.

Thanks,

tglx

Yuntao Wang

author

2024-08-13 01:48 UTC #4 lore raw

PATCH v2 1/1 x86/apic: Fix the issues in x2apic_disable()

There are two issues in x2apic_disable().

Therefore, 'if (state != X2APIC_ON)' should be changed to 'if (state < X2APIC_ON)', so that when x2apic_state is X2APIC_ON_LOCKED, the corresponding warning log can be printed.

Let's fix these issues.

Signed-off-by Yuntao Wang <[email protected]>

---
v1->v2: Modify according to Thomas Gleixner's suggestion.

 arch/x86/kernel/apic/apic.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

arch/x86/kernel/apic/apic.c +5 -5

index 66fd4b2a37a3..50acd094b055 100644
@@ -1775,12 +1775,9 @@ static __init void apic_set_fixmap(bool read_apic);
 
 static __init void x2apic_disable(void)
 {
-	u32 x2apic_id, state = x2apic_state;
+	u32 x2apic_id;
 
-	x2apic_mode = 0;
-	x2apic_state = X2APIC_DISABLED;
-
-	if (state != X2APIC_ON)
+	if (x2apic_state < X2APIC_ON)
 		return;
 
 	x2apic_id = read_apic_id();

@@ -1799,6 +1796,9 @@ static __init void x2apic_disable(void)
 	 * which fails to do the read after x2APIC was disabled.
 	 */
 	apic_set_fixmap(false);
+
+	x2apic_mode = 0;
+	x2apic_state = X2APIC_DISABLED;
 }
 
 static __init void x2apic_enable(void)

Signature · 1 line

2.46.0

tip-bot2 for Yuntao Wang

merge bot Applied

2024-08-13 13:21 UTC #5 lore raw

[tip: x86/urgent] x86/apic: Make x2apic_disable() work correctly

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     0ecc5be200c84e67114f3640064ba2bae3ba2f5a
Gitweb:        https://git.kernel.org/tip/0ecc5be200c84e67114f3640064ba2bae3ba2f5a
Author:        Yuntao Wang <[email protected]>
AuthorDate:    Tue, 13 Aug 2024 09:48:27 +08:00
Committer:     Thomas Gleixner <[email protected]>
CommitterDate: Tue, 13 Aug 2024 15:15:19 +02:00

x86/apic: Make x2apic_disable() work correctly

x2apic_disable() clears x2apic_state and x2apic_mode unconditionally, even when the state is X2APIC_ON_LOCKED, which prevents the kernel to disable it thereby creating inconsistent state.

Due to the early state check for X2APIC_ON, the code path which warns about a locked X2APIC cannot be reached.

Test for state < X2APIC_ON instead and move the clearing of the state and mode variables to the place which actually disables X2APIC.

[ tglx: Massaged change log. Added Fixes tag. Moved clearing so it's at the
right place for back ports ]

Fixes a57e456a7b28 ("x86/apic: Fix fallout from x2apic cleanup")

Signed-off-by Yuntao Wang <[email protected]>

Signed-off-by Thomas Gleixner <[email protected]>

Cc [email protected]

Link https://lore.kernel.org/all/[email protected] open here

---
 arch/x86/kernel/apic/apic.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

arch/x86/kernel/apic/apic.c +6 -5

index 66fd4b2..3736386 100644
@@ -1775,12 +1775,9 @@ static __init void apic_set_fixmap(bool read_apic);
 
 static __init void x2apic_disable(void)
 {
-	u32 x2apic_id, state = x2apic_state;
+	u32 x2apic_id;
 
-	x2apic_mode = 0;
-	x2apic_state = X2APIC_DISABLED;
-
-	if (state != X2APIC_ON)
+	if (x2apic_state < X2APIC_ON)
 		return;
 
 	x2apic_id = read_apic_id();

@@ -1793,6 +1790,10 @@ static __init void x2apic_disable(void)
 	}
 
 	__x2apic_disable();
+
+	x2apic_mode = 0;
+	x2apic_state = X2APIC_DISABLED;
+
 	/*
 	 * Don't reread the APIC ID as it was already done from
 	 * check_x2apic() and the APIC driver still is a x2APIC variant,