Re: [PATCH 04/13] x86/x2apic: Support x2apic self IPI with NMI_VECTOR

From: Ashok Raj
Date: Wed Oct 19 2022 - 11:43:35 EST


On Fri, Oct 14, 2022 at 01:09:04PM -0700, Ashok Raj wrote:
> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
>
> X2APIC architecture introduced a dedicated register for sending self-IPI.
> Though highly optimized for performance, its semantics limit the delivery
> mode to fixed mode. NMI vector is not supported, this created an
> inconsistent behavior between X2APIC and others.
>
> This patch adds support for X2APIC NMI_VECTOR by fall back to the slower
> ICR method.
>
> Suggested-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>

Forgot to add my sob here.. I;ll fix it in the resend.
> ---
> arch/x86/kernel/apic/x2apic_phys.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
> index 6bde05a86b4e..5f533b76adf6 100644
> --- a/arch/x86/kernel/apic/x2apic_phys.c
> +++ b/arch/x86/kernel/apic/x2apic_phys.c
> @@ -149,7 +149,11 @@ int x2apic_phys_pkg_id(int initial_apicid, int index_msb)
>
> void x2apic_send_IPI_self(int vector)
> {
> - apic_write(APIC_SELF_IPI, vector);
> + if (vector == NMI_VECTOR)
> + apic->send_IPI_mask(cpumask_of(smp_processor_id()),
> + NMI_VECTOR);
> + else
> + apic_write(APIC_SELF_IPI, vector);
> }

Wanted to send this early if people are planning to test

Similar helper is required for legacy xapic as well. The lack of it helped
test the timeout path's :-).. I'll integrated it when i send the next round
with feedback once i have enough. I'll also send this in the next update.

diff --git a/arch/x86/kernel/apic/ipi.c b/arch/x86/kernel/apic/ipi.c
index 2a6509e8c840..e967c49609ef 100644
--- a/arch/x86/kernel/apic/ipi.c
+++ b/arch/x86/kernel/apic/ipi.c
@@ -239,7 +239,11 @@ void default_send_IPI_all(int vector)

void default_send_IPI_self(int vector)
{
- __default_send_IPI_shortcut(APIC_DEST_SELF, vector);
+ if (unlikely(vector == NMI_VECTOR))
+ apic->send_IPI_mask(cpumask_of(smp_processor_id()),
+ NMI_VECTOR);
+ else
+ __default_send_IPI_shortcut(APIC_DEST_SELF, vector);
}

#ifdef CONFIG_X86_32



>
> static struct apic apic_x2apic_phys __ro_after_init = {
> --
> 2.34.1
>