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Date: Sun, 24 Oct 2010 12:15:27 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Yinghai Lu <yinghai@...nel.org>
cc: Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/15] x86: Disabling x2apic if nox2apic is specified
On Sat, 23 Oct 2010, Yinghai Lu wrote:
> For
> 1. x2apic preenabled system
> 2. first kernel have x2apic enabled, and try to boot second kernel with "nox2apic"
>
> Will put back cpu with apic id < 255 into xapic mode, instead of panic.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
> arch/x86/include/asm/apic.h | 6 ++++
> arch/x86/include/asm/apicdef.h | 1 +
> arch/x86/kernel/acpi/boot.c | 10 ++++++-
> arch/x86/kernel/apic/apic.c | 54 +++++++++++++++++++++++++++++++--------
> arch/x86/mm/srat_64.c | 12 ++++++++-
> 5 files changed, 69 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 69879dd..522f39b 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -176,6 +176,7 @@ static inline u64 native_x2apic_icr_read(void)
> }
>
> extern int x2apic_phys;
> +extern int nox2apic;
Can you please use a sensible variable name like x2apic_disabled ?
> extern void check_x2apic(void);
> extern void enable_x2apic(void);
> extern void x2apic_icr_write(u32 low, u32 id);
> @@ -186,6 +187,10 @@ static inline int x2apic_enabled(void)
> if (!cpu_has_x2apic)
> return 0;
>
> + /* avoid to read msr */
That comment is useless. I wish you would add comments to complex code
not to obvious one.
Also it can be folded into the above check
if (!cpu_has_x2apic || x2apic_disabled)
> + if (nox2apic)
> + return 0;
> +
> rdmsr(MSR_IA32_APICBASE, msr, msr2);
> if (msr & X2APIC_ENABLE)
> return 1;
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index d286db1..ebb13e8 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -138,15 +138,14 @@ int x2apic_mode;
> #ifdef CONFIG_X86_X2APIC
> /* x2apic enabled before OS handover */
> static int x2apic_preenabled;
> +int nox2apic;
> static __init int setup_nox2apic(char *str)
> {
> - if (x2apic_enabled()) {
> - pr_warning("Bios already enabled x2apic, "
> - "can't enforce nox2apic");
> - return 0;
> - }
> + if (x2apic_enabled())
> + pr_warning("Bios already enabled x2apic, will disable it");
> +
> + nox2apic = 1;
>
> - setup_clear_cpu_cap(X86_FEATURE_X2APIC);
Why is this removed ?
> return 0;
> }
> early_param("nox2apic", setup_nox2apic);
> @@ -1393,8 +1392,33 @@ void __cpuinit end_local_APIC_setup(void)
> }
>
> #ifdef CONFIG_X86_X2APIC
> +
> +static void disable_x2apic(void)
> +{
> + int msr, msr2;
> +
> + if (!cpu_has_x2apic)
> + return;
> +
> + rdmsr(MSR_IA32_APICBASE, msr, msr2);
> + if (msr & X2APIC_ENABLE) {
> + pr_info("Disabling x2apic\n");
> + /*
> + * Need to disable xapic and x2apic at the same time at first
> + * then enable xapic
> + */
> + wrmsr(MSR_IA32_APICBASE, msr & ~(X2APIC_ENABLE | XAPIC_ENABLE),
> + 0);
> + wrmsr(MSR_IA32_APICBASE, msr & ~X2APIC_ENABLE, 0);
> + }
> +}
> void check_x2apic(void)
> {
> + if (nox2apic) {
> + disable_x2apic();
> + return;
> + }
> +
> if (x2apic_enabled()) {
> pr_info("x2apic enabled by BIOS, switching to x2apic ops\n");
> x2apic_preenabled = x2apic_mode = 1;
> @@ -1405,6 +1429,11 @@ void enable_x2apic(void)
> {
> int msr, msr2;
>
> + if (nox2apic) {
> + disable_x2apic();
> + return;
> + }
> +
> if (!x2apic_mode)
> return;
>
> @@ -1430,7 +1459,7 @@ int __init enable_IR(void)
> return 0;
> }
>
> - if (enable_intr_remapping(x2apic_supported()))
> + if (enable_intr_remapping(x2apic_supported() && !nox2apic))
Do we really need all these extra checks ? Can't we simply make all
this one variable wich is set to 1 when x2apic is available and not
disabled on the kernel command line ?
> diff --git a/arch/x86/mm/srat_64.c b/arch/x86/mm/srat_64.c
> index a35cb9d..baa9eab 100644
> --- a/arch/x86/mm/srat_64.c
> +++ b/arch/x86/mm/srat_64.c
> @@ -126,6 +126,13 @@ acpi_numa_x2apic_affinity_init(struct acpi_srat_x2apic_cpu_affinity *pa)
> if ((pa->flags & ACPI_SRAT_CPU_ENABLED) == 0)
> return;
> pxm = pa->proximity_domain;
> + apic_id = pa->apic_id;
> +#ifdef CONFIG_X86_X2APIC
Why conditional? No need to duplicate the printk. It just needs some
thought.
> + if (nox2apic && (apic_id >= 0xff)) {
> + printk(KERN_INFO "SRAT: PXM %u -> X2APIC 0x%04x ignored\n",
> + pxm, apic_id);
> + return;
> + }
> node = setup_node(pxm);
> if (node < 0) {
> printk(KERN_ERR "SRAT: Too many proximity domains %x\n", pxm);
> @@ -133,12 +140,15 @@ acpi_numa_x2apic_affinity_init(struct acpi_srat_x2apic_cpu_affinity *pa)
> return;
> }
>
> - apic_id = pa->apic_id;
> apicid_to_node[apic_id] = node;
> node_set(node, cpu_nodes_parsed);
> acpi_numa = 1;
> printk(KERN_INFO "SRAT: PXM %u -> APIC 0x%04x -> Node %u\n",
> pxm, apic_id, node);
> +#else
> + printk(KERN_INFO "SRAT: PXM %u -> X2APIC 0x%04x ignored\n",
> + pxm, apic_id);
> +#endif
> }
>
> /* Callback for Proximity Domain -> LAPIC mapping */
> --
> 1.7.1
>
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