linux-kernel - Re: [PATCH] x86/build: Build VSMP support only if selected

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Date:   Thu, 1 Nov 2018 17:09:50 +0200
From:   Eial Czerwacki <eial@...lemp.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Shai Fultheim (Shai@...leMP.com)" <Shai@...leMP.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "mhocko@...e.cz" <mhocko@...e.cz>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "mm-commits@...r.kernel.org" <mm-commits@...r.kernel.org>,
        X86 ML <x86@...nel.org>, 'Oren Twaig' <oren@...lemp.com>
Subject: Re: [PATCH] x86/build: Build VSMP support only if selected

Greetings,

On 11/01/2018 03:45 PM, Juergen Gross wrote:
> On 01/11/2018 14:10, Eial Czerwacki wrote:
>> Greetings,
>>
>> On 11/01/2018 12:39 PM, Shai Fultheim (Shai@...leMP.com) wrote:
>>> On 01/11/18 11:37, Thomas Gleixner wrote:
>>>
>>>> VSMP support is built even if CONFIG_X86_VSMP is not set. This leads to a build
>>>> breakage when CONFIG_PCI is disabled as well.
>>>>
>>>> Build VSMP code only when selected.
>>>
>>> This patch disables detect_vsmp_box() on systems without CONFIG_X86_VSMP, due to
>>> the recent 6da63eb241a05b0e676d68975e793c0521387141.  This is significant
>>> regression that will affect significant number of deployments.
>>>
>>> We will reply shortly with an updated patch that fix the dependency on pv_irq_ops,
>>> and revert to CONFIG_PARAVIRT, with proper protection for CONFIG_PCI.
>>>
>>
>> here is the proper patch which fixes the issue on hand:
>> From ebff534f8cfa55d7c3ab798c44abe879f3fbe2b8 Mon Sep 17 00:00:00 2001
>> From: Eial Czerwacki <eial@...lemp.com>
>> Date: Thu, 1 Nov 2018 15:08:32 +0200
>> Subject: [PATCH] x86/build: Build VSMP support only if CONFIG_PCI is
>> selected
>>
>> vsmp dependency of pv_irq_ops removed some years ago, so now let's clean
>> it up from vsmp_64.c.
>>
>> In short, "cap & ctl & (1 << 4)" was always returning 0, as such we can
>> remove all the PARAVIRT/PARAVIRT_XXL code handling that.
>>
>> However, the rest of the code depends on CONFIG_PCI, so fix it accordingly.
>>
>> Signed-off-by: Eial Czerwacki <eial@...lemp.com>
>> Acked-by: Shai Fultheim <shai@...lemp.com>
>> ---
>>  arch/x86/Kconfig          |  1 -
>>  arch/x86/kernel/vsmp_64.c | 80
>> +++--------------------------------------------
>>  2 files changed, 5 insertions(+), 76 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index c51c989..4b187ca 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -524,7 +524,6 @@ config X86_VSMP
>>         bool "ScaleMP vSMP"
>>         select HYPERVISOR_GUEST
>>         select PARAVIRT
> 
> Do you really still need PARAVIRT and HYPERVISOR_GUEST?
> Maybe you want IRQ_REMAP instead?
> 
Better performance is achieved with PARAVIRTed kernel.   Hence we keep
them both in.

>> -       select PARAVIRT_XXL
>>         depends on X86_64 && PCI
>>         depends on X86_EXTENDED_PLATFORM
>>         depends on SMP
>> diff --git a/arch/x86/kernel/vsmp_64.c b/arch/x86/kernel/vsmp_64.c
>> index 1eae5af..c6d2b76 100644
>> --- a/arch/x86/kernel/vsmp_64.c
>> +++ b/arch/x86/kernel/vsmp_64.c
>> @@ -26,64 +26,7 @@
>>
>>  #define TOPOLOGY_REGISTER_OFFSET 0x10
>>
>> -#if defined CONFIG_PCI && defined CONFIG_PARAVIRT_XXL
>> -/*
>> - * Interrupt control on vSMPowered systems:
>> - * ~AC is a shadow of IF.  If IF is 'on' AC should be 'off'
>> - * and vice versa.
>> - */
>> -
>> -asmlinkage __visible unsigned long vsmp_save_fl(void)
>> -{
>> -       unsigned long flags = native_save_fl();
>> -
>> -       if (!(flags & X86_EFLAGS_IF) || (flags & X86_EFLAGS_AC))
>> -               flags &= ~X86_EFLAGS_IF;
>> -       return flags;
>> -}
>> -PV_CALLEE_SAVE_REGS_THUNK(vsmp_save_fl);
>> -
>> -__visible void vsmp_restore_fl(unsigned long flags)
>> -{
>> -       if (flags & X86_EFLAGS_IF)
>> -               flags &= ~X86_EFLAGS_AC;
>> -       else
>> -               flags |= X86_EFLAGS_AC;
>> -       native_restore_fl(flags);
>> -}
>> -PV_CALLEE_SAVE_REGS_THUNK(vsmp_restore_fl);
>> -
>> -asmlinkage __visible void vsmp_irq_disable(void)
>> -{
>> -       unsigned long flags = native_save_fl();
>> -
>> -       native_restore_fl((flags & ~X86_EFLAGS_IF) | X86_EFLAGS_AC);
>> -}
>> -PV_CALLEE_SAVE_REGS_THUNK(vsmp_irq_disable);
>> -
>> -asmlinkage __visible void vsmp_irq_enable(void)
>> -{
>> -       unsigned long flags = native_save_fl();
>> -
>> -       native_restore_fl((flags | X86_EFLAGS_IF) & (~X86_EFLAGS_AC));
>> -}
>> -PV_CALLEE_SAVE_REGS_THUNK(vsmp_irq_enable);
>> -
>> -static unsigned __init vsmp_patch(u8 type, void *ibuf,
>> -                                 unsigned long addr, unsigned len)
>> -{
>> -       switch (type) {
>> -       case PARAVIRT_PATCH(irq.irq_enable):
>> -       case PARAVIRT_PATCH(irq.irq_disable):
>> -       case PARAVIRT_PATCH(irq.save_fl):
>> -       case PARAVIRT_PATCH(irq.restore_fl):
>> -               return paravirt_patch_default(type, ibuf, addr, len);
>> -       default:
>> -               return native_patch(type, ibuf, addr, len);
>> -       }
>> -
>> -}
>> -
>> +#if defined CONFIG_PCI
>>  static void __init set_vsmp_pv_ops(void)
> 
> Wouldn't be a rename of the function be appropriate now?
you are correct, I'll fix and resend the patch.

> 
> 
> Juergen
>