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

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Message-ID: <054cd800-5124-f897-0069-aba49f8eb654@suse.com>
Date:   Thu, 1 Nov 2018 14:45:05 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Eial Czerwacki <eial@...lemp.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Randy Dunlap <rdunlap@...radead.org>
Cc:     "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

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?

> -       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?


Juergen