linux-kernel - Re: [patch V2 50/58] x86/apic: Provide common init infrastructure

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Date:   Tue, 01 Aug 2023 09:30:39 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Juergen Gross <jgross@...e.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andrew Cooper <andrew.cooper3@...rix.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wei Liu <wei.liu@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Peter Keresztes Schmidt <peter@...esztesschmidt.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V2 50/58] x86/apic: Provide common init infrastructure

On Tue, Aug 01 2023 at 08:41, Thomas Gleixner wrote:

> On Mon, Jul 31 2023 at 17:48, Thomas Gleixner wrote:
>
>> On Mon, Jul 31 2023 at 15:10, Juergen Gross wrote:
>>> On 31.07.23 15:01, Thomas Gleixner wrote:
>>>>>    apic_driver(xen_pv_apic);
>>>> 
>>>> I wonder whether this explicit install is actually needed at all.
>>>> Shouldn't the driver be installed via the APIC probing mechanism
>>>> automagically?
>>>
>>> Only in case x86_init.irq.intr_mode_init is set appropriately. Today it is
>>> a nop for Xen PV, but that can be changed. I'll have a look.
>>
>> You could simply set that callback to default_setup_apic_routing() and
>> be done with it.
>
> Doesn't work because XEN overrides it already. So sure, lets just go
> with the solution you proposed. One more ugly or less in XEN/PV does not
> really matter much :)
>
> Let me grab this and put it into the right position in the queue.

Spoke too early. The below should work AFAICT from the code.


--- a/arch/x86/xen/apic.c
+++ b/arch/x86/xen/apic.c
@@ -99,10 +99,7 @@ static void xen_apic_icr_write(u32 low,
 
 static int xen_apic_probe_pv(void)
 {
-	if (xen_pv_domain())
-		return 1;
-
-	return 0;
+	return xen_pv_domain();
 }
 
 static int xen_madt_oem_check(char *oem_id, char *oem_table_id)
@@ -157,20 +154,14 @@ static struct apic xen_pv_apic = {
 	.icr_read 			= xen_apic_icr_read,
 	.icr_write 			= xen_apic_icr_write,
 };
-
-static void __init xen_apic_check(void)
-{
-	apic_install_driver(&xen_pv_apic);
-}
+apic_driver(xen_pv_apic);
 
 void __init xen_init_apic(void)
 {
 	x86_apic_ops.io_apic_read = xen_io_apic_read;
-	/* On PV guests the APIC CPUID bit is disabled so none of the
-	 * routines end up executing. */
-	if (!xen_initial_domain())
-		apic_install_driver(&xen_pv_apic);
-
-	x86_platform.apic_post_init = xen_apic_check;
+	/*
+	 * On PV guests the APIC CPUID bit is disabled so none of the
+	 * routines end up executing.
+	 */
+	apic_install_driver(&xen_pv_apic);
 }
-apic_driver(xen_pv_apic);
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1325,7 +1325,7 @@ asmlinkage __visible void __init xen_sta
 	x86_platform.realmode_init = x86_init_noop;
 
 	x86_init.resources.memory_setup = xen_memory_setup;
-	x86_init.irqs.intr_mode_select	= x86_init_noop;
+	x86_init.irqs.intr_mode_select	= xen_init_apic;
 	x86_init.irqs.intr_mode_init	= x86_init_noop;
 	x86_init.oem.arch_setup = xen_arch_setup;
 	x86_init.oem.banner = xen_banner;
@@ -1366,13 +1366,6 @@ asmlinkage __visible void __init xen_sta
 
 	xen_init_capabilities();
 
-#ifdef CONFIG_X86_LOCAL_APIC
-	/*
-	 * set up the basic apic ops.
-	 */
-	xen_init_apic();
-#endif
-
 	machine_ops = xen_machine_ops;
 
 	/*
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -118,7 +118,11 @@ static inline void __init xen_init_vga(c
 
 void xen_add_preferred_consoles(void);
 
+#ifdef CONFIG_X86_LOCAL_APIC
 void __init xen_init_apic(void);
+#else
+# define xen_init_apic	x86_init_noop
+#endif
 
 #ifdef CONFIG_XEN_EFI
 extern void xen_efi_init(struct boot_params *boot_params);