linux-kernel - Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT

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Date:   Wed, 12 May 2021 15:51:24 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL

On 12.05.21 15:24, Andi Kleen wrote:
> 
> On 5/12/2021 6:18 AM, Peter Zijlstra wrote:
>> On Mon, May 10, 2021 at 05:56:05PM +0200, Juergen Gross wrote:
>>
>>> No. We have PARAVIRT_XXL for Xen PV guests, and we have PARAVIRT for
>>> other hypervisor's guests, supporting basically the TLB flush operations
>>> and time related operations only. Adding the halt related operations to
>>> PARAVIRT wouldn't break anything.
>> Also, I don't think anything modern should actually ever hit any of the
>> HLT instructions, most everything should end up at an MWAIT.
>>
>> Still, do we wants to give arch_safe_halt() and halt() the
>> PVOP_ALT_VCALL0() treatment?
> 
>  From performance reasons it's pointless to patch. HLT (and MWAIT) are 
> so slow anyways that using patching or an indirect pointer is completely 
> in the noise. So I would use whatever is cleanest in the code.

This would probably be x86_platform_ops.hyper hooks.


Juergen

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