[PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[Saurabh Sengar]

arch_dynirq_lower_bound() is invoked by the core interrupt code to
retrieve the lowest possible Linux interrupt number for dynamically
allocated interrupts like MSI.

The x86 implementation uses this to exclude the IO/APIC GSI space.
This works correctly as long as there is an IO/APIC registered, but
returns 0 if not. This has been observed in VMs where the BIOS does
not advertise an IO/APIC.

0 is an invalid interrupt number except for the legacy timer interrupt
on x86. The return value is unchecked in the core code, so it ends up
to allocate interrupt number 0 which is subsequently considered to be
invalid by the caller, e.g. the MSI allocation code.

The function has already a check for 0 in the case that an IO/APIC is
registered, but ioapic_dynirq_base is 0 in case of device tree setups.

Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
which is used in the case that no IO/APIC is registered.

Fixes: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Cc: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
[V2]
- Edit commit message
- Consolidated the 0 check for ioapic_dynirq_base as well

 arch/x86/kernel/apic/io_apic.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 1f83b052bb74..f980b38b0227 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2477,17 +2477,21 @@ static int io_apic_get_redir_entries(int ioapic)
 
 unsigned int arch_dynirq_lower_bound(unsigned int from)
 {
+	unsigned int ret;
+
 	/*
 	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
 	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
 	 */
-	if (!ioapic_initialized)
-		return gsi_top;
+	ret = ioapic_dynirq_base ? : gsi_top;
+
 	/*
-	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
-	 * updated. So simply return @from if ioapic_dynirq_base == 0.
+	 * For DT enabled machines ioapic_dynirq_base is irrelevant and
+	 * always 0. gsi_top can be 0 if there is no IO/APIC registered.
+	 * 0 is an invalid interrupt number for dynamic allocations. Return
+	 * @from instead.
 	 */
-	return ioapic_dynirq_base ? : from;
+	return ret ? : from;
 }
 
 #ifdef CONFIG_X86_32
-- 
2.34.1

Re: [PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[H. Peter Anvin]

On March 28, 2023 12:30:04 AM PDT, Saurabh Sengar <ssengar@linux.microsoft.com> wrote:
>arch_dynirq_lower_bound() is invoked by the core interrupt code to
>retrieve the lowest possible Linux interrupt number for dynamically
>allocated interrupts like MSI.
>
>The x86 implementation uses this to exclude the IO/APIC GSI space.
>This works correctly as long as there is an IO/APIC registered, but
>returns 0 if not. This has been observed in VMs where the BIOS does
>not advertise an IO/APIC.
>
>0 is an invalid interrupt number except for the legacy timer interrupt
>on x86. The return value is unchecked in the core code, so it ends up
>to allocate interrupt number 0 which is subsequently considered to be
>invalid by the caller, e.g. the MSI allocation code.
>
>The function has already a check for 0 in the case that an IO/APIC is
>registered, but ioapic_dynirq_base is 0 in case of device tree setups.
>
>Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
>which is used in the case that no IO/APIC is registered.
>
>Fixes: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
>Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
>Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
>Cc: Andy Shevchenko <andriy.shevchenko@intel.com>
>Cc: Thomas Gleixner <tglx@linutronix.de>
>---
>[V2]
>- Edit commit message
>- Consolidated the 0 check for ioapic_dynirq_base as well
>
> arch/x86/kernel/apic/io_apic.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
>diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
>index 1f83b052bb74..f980b38b0227 100644
>--- a/arch/x86/kernel/apic/io_apic.c
>+++ b/arch/x86/kernel/apic/io_apic.c
>@@ -2477,17 +2477,21 @@ static int io_apic_get_redir_entries(int ioapic)
> 
> unsigned int arch_dynirq_lower_bound(unsigned int from)
> {
>+	unsigned int ret;
>+
> 	/*
> 	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
> 	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
> 	 */
>-	if (!ioapic_initialized)
>-		return gsi_top;
>+	ret = ioapic_dynirq_base ? : gsi_top;
>+
> 	/*
>-	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
>-	 * updated. So simply return @from if ioapic_dynirq_base == 0.
>+	 * For DT enabled machines ioapic_dynirq_base is irrelevant and
>+	 * always 0. gsi_top can be 0 if there is no IO/APIC registered.
>+	 * 0 is an invalid interrupt number for dynamic allocations. Return
>+	 * @from instead.
> 	 */
>-	return ioapic_dynirq_base ? : from;
>+	return ret ? : from;
> }
> 
> #ifdef CONFIG_X86_32

Is there any reason why this variable can't be initialized to a fixed nonzero number, like 16?

Re: [PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[Saurabh Singh Sengar]

On Tue, Mar 28, 2023 at 06:59:04AM -0700, H. Peter Anvin wrote:
> On March 28, 2023 12:30:04 AM PDT, Saurabh Sengar <ssengar@linux.microsoft.com> wrote:
> >arch_dynirq_lower_bound() is invoked by the core interrupt code to
> >retrieve the lowest possible Linux interrupt number for dynamically
> >allocated interrupts like MSI.
> >
> >The x86 implementation uses this to exclude the IO/APIC GSI space.
> >This works correctly as long as there is an IO/APIC registered, but
> >returns 0 if not. This has been observed in VMs where the BIOS does
> >not advertise an IO/APIC.
> >
> >0 is an invalid interrupt number except for the legacy timer interrupt
> >on x86. The return value is unchecked in the core code, so it ends up
> >to allocate interrupt number 0 which is subsequently considered to be
> >invalid by the caller, e.g. the MSI allocation code.
> >
> >The function has already a check for 0 in the case that an IO/APIC is
> >registered, but ioapic_dynirq_base is 0 in case of device tree setups.
> >
> >Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
> >which is used in the case that no IO/APIC is registered.
> >
> >Fixes: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
> >Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
> >Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> >Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> >Cc: Andy Shevchenko <andriy.shevchenko@intel.com>
> >Cc: Thomas Gleixner <tglx@linutronix.de>
> >---
> >[V2]
> >- Edit commit message
> >- Consolidated the 0 check for ioapic_dynirq_base as well
> >
> > arch/x86/kernel/apic/io_apic.c | 14 +++++++++-----
> > 1 file changed, 9 insertions(+), 5 deletions(-)
> >
> >diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> >index 1f83b052bb74..f980b38b0227 100644
> >--- a/arch/x86/kernel/apic/io_apic.c
> >+++ b/arch/x86/kernel/apic/io_apic.c
> >@@ -2477,17 +2477,21 @@ static int io_apic_get_redir_entries(int ioapic)
> > 
> > unsigned int arch_dynirq_lower_bound(unsigned int from)
> > {
> >+	unsigned int ret;
> >+
> > 	/*
> > 	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
> > 	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
> > 	 */
> >-	if (!ioapic_initialized)
> >-		return gsi_top;
> >+	ret = ioapic_dynirq_base ? : gsi_top;
> >+
> > 	/*
> >-	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
> >-	 * updated. So simply return @from if ioapic_dynirq_base == 0.
> >+	 * For DT enabled machines ioapic_dynirq_base is irrelevant and
> >+	 * always 0. gsi_top can be 0 if there is no IO/APIC registered.
> >+	 * 0 is an invalid interrupt number for dynamic allocations. Return
> >+	 * @from instead.
> > 	 */
> >-	return ioapic_dynirq_base ? : from;
> >+	return ret ? : from;
> > }
> > 
> > #ifdef CONFIG_X86_32
> 
> Is there any reason why this variable can't be initialized to a fixed nonzero number, like 16?

Yes, initializing gst_top to any non-zero value should fix this issue.
At first I thought to intialize gst_top to 1. But then I looked at how
the ioapic_dynirq_base case is handled and followed a similar approach.

Regards,
Saurabh

Re: [PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[Thomas Gleixner]

On Tue, Mar 28 2023 at 07:48, Saurabh Singh Sengar wrote:
> On Tue, Mar 28, 2023 at 06:59:04AM -0700, H. Peter Anvin wrote:
>> 
>> Is there any reason why this variable can't be initialized to a fixed nonzero number, like 16?
>
> Yes, initializing gst_top to any non-zero value should fix this issue.
> At first I thought to intialize gst_top to 1.

That works only in your case. Some boot time registrations of IO_APICs
use gsi_top as the base. So initializing gsi_top to N would move IOAPIC[0]
interrupts out to irq N... and make the legacy interrupts fail.

That whole IOAPIC registration could do with some major cleanup, but
that's a different story.

Thanks,

        tglx

Re: [PATCH v2] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[Saurabh Singh Sengar]

On Tue, Mar 28, 2023 at 12:30:04AM -0700, Saurabh Sengar wrote:
> arch_dynirq_lower_bound() is invoked by the core interrupt code to
> retrieve the lowest possible Linux interrupt number for dynamically
> allocated interrupts like MSI.
> 
> The x86 implementation uses this to exclude the IO/APIC GSI space.
> This works correctly as long as there is an IO/APIC registered, but
> returns 0 if not. This has been observed in VMs where the BIOS does
> not advertise an IO/APIC.
> 
> 0 is an invalid interrupt number except for the legacy timer interrupt
> on x86. The return value is unchecked in the core code, so it ends up
> to allocate interrupt number 0 which is subsequently considered to be
> invalid by the caller, e.g. the MSI allocation code.
> 
> The function has already a check for 0 in the case that an IO/APIC is
> registered, but ioapic_dynirq_base is 0 in case of device tree setups.
> 
> Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
> which is used in the case that no IO/APIC is registered.
> 
> Fixes: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
> Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> Cc: Andy Shevchenko <andriy.shevchenko@intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
> [V2]
> - Edit commit message
> - Consolidated the 0 check for ioapic_dynirq_base as well
> 
>  arch/x86/kernel/apic/io_apic.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index 1f83b052bb74..f980b38b0227 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2477,17 +2477,21 @@ static int io_apic_get_redir_entries(int ioapic)
>  
>  unsigned int arch_dynirq_lower_bound(unsigned int from)
>  {
> +	unsigned int ret;
> +
>  	/*
>  	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
>  	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
>  	 */
> -	if (!ioapic_initialized)
> -		return gsi_top;
> +	ret = ioapic_dynirq_base ? : gsi_top;
> +
>  	/*
> -	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
> -	 * updated. So simply return @from if ioapic_dynirq_base == 0.
> +	 * For DT enabled machines ioapic_dynirq_base is irrelevant and
> +	 * always 0. gsi_top can be 0 if there is no IO/APIC registered.
> +	 * 0 is an invalid interrupt number for dynamic allocations. Return
> +	 * @from instead.
>  	 */
> -	return ioapic_dynirq_base ? : from;
> +	return ret ? : from;
>  }
>  
>  #ifdef CONFIG_X86_32

Is this good to get accepted ? Please let me know if anything pending from my end on this.

- Saurabh

> -- 
> 2.34.1

[tip: x86/apic] x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[tip-bot2 for Saurabh Sengar]

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

Commit-ID:     5af507bef93c09a94fb8f058213b489178f4cbe5
Gitweb:        https://git.kernel.org/tip/5af507bef93c09a94fb8f058213b489178f4cbe5
Author:        Saurabh Sengar <ssengar@linux.microsoft.com>
AuthorDate:    Tue, 28 Mar 2023 00:30:04 -07:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 12 Apr 2023 17:45:50 +02:00

x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

arch_dynirq_lower_bound() is invoked by the core interrupt code to
retrieve the lowest possible Linux interrupt number for dynamically
allocated interrupts like MSI.

The x86 implementation uses this to exclude the IO/APIC GSI space.
This works correctly as long as there is an IO/APIC registered, but
returns 0 if not. This has been observed in VMs where the BIOS does
not advertise an IO/APIC.

0 is an invalid interrupt number except for the legacy timer interrupt
on x86. The return value is unchecked in the core code, so it ends up
to allocate interrupt number 0 which is subsequently considered to be
invalid by the caller, e.g. the MSI allocation code.

The function has already a check for 0 in the case that an IO/APIC is
registered, as ioapic_dynirq_base is 0 in case of device tree setups.

Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
which is used in the case that no IO/APIC is registered.

Fixes: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/1679988604-20308-1-git-send-email-ssengar@linux.microsoft.com

---
 arch/x86/kernel/apic/io_apic.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 1f83b05..f980b38 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2477,17 +2477,21 @@ static int io_apic_get_redir_entries(int ioapic)
 
 unsigned int arch_dynirq_lower_bound(unsigned int from)
 {
+	unsigned int ret;
+
 	/*
 	 * dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
 	 * gsi_top if ioapic_dynirq_base hasn't been initialized yet.
 	 */
-	if (!ioapic_initialized)
-		return gsi_top;
+	ret = ioapic_dynirq_base ? : gsi_top;
+
 	/*
-	 * For DT enabled machines ioapic_dynirq_base is irrelevant and not
-	 * updated. So simply return @from if ioapic_dynirq_base == 0.
+	 * For DT enabled machines ioapic_dynirq_base is irrelevant and
+	 * always 0. gsi_top can be 0 if there is no IO/APIC registered.
+	 * 0 is an invalid interrupt number for dynamic allocations. Return
+	 * @from instead.
 	 */
-	return ioapic_dynirq_base ? : from;
+	return ret ? : from;
 }
 
 #ifdef CONFIG_X86_32