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Subject: Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL
To:     Andi Kleen <ak@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Borislav Petkov <bp@alien8.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Raj Ashok <ashok.raj@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        linux-kernel@vger.kernel.org
References: <cover.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com>
 <4f8c9559dd04d8e8485c419c5ebc9471613f7928.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com>
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 <a24884ac-452e-751f-fb3e-82b3a9978ed1@linux.intel.com>
 <41463493-48bb-0e69-dcb2-3072e2ddf208@suse.com>
 <YJvVwXqGZWrXWPvP@hirez.programming.kicks-ass.net>
 <f1ae9d97-a23e-d902-4ddb-6ec7b5d8cb91@linux.intel.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <28f5b8c2-2307-45b0-19b4-0737df8f06f3@suse.com>
Date:   Wed, 12 May 2021 15:51:24 +0200
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From: Juergen Gross <jgross@suse.com>
To: Andi Kleen <ak@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 Andy Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@intel.com>,
 Dan Williams <dan.j.williams@intel.com>, Tony Luck <tony.luck@intel.com>,
 Kirill Shutemov <kirill.shutemov@linux.intel.com>,
 Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
 Raj Ashok <ashok.raj@intel.com>, Sean Christopherson <seanjc@google.com>,
 linux-kernel@vger.kernel.org
Message-ID: <28f5b8c2-2307-45b0-19b4-0737df8f06f3@suse.com>
Subject: Re: [RFC v2 01/32] x86/paravirt: Introduce CONFIG_PARAVIRT_XL
References: <cover.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com>
 <4f8c9559dd04d8e8485c419c5ebc9471613f7928.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com>
 <YIhKXcNuinL0ar0O@zn.tnic> <f62354fe-e202-ad38-5466-03e79954f757@suse.com>
 <a24884ac-452e-751f-fb3e-82b3a9978ed1@linux.intel.com>
 <41463493-48bb-0e69-dcb2-3072e2ddf208@suse.com>
 <YJvVwXqGZWrXWPvP@hirez.programming.kicks-ass.net>
 <f1ae9d97-a23e-d902-4ddb-6ec7b5d8cb91@linux.intel.com>
In-Reply-To: <f1ae9d97-a23e-d902-4ddb-6ec7b5d8cb91@linux.intel.com>

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On 12.05.21 15:24, Andi Kleen wrote:
>=20
> 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 operati=
ons
>>> 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 th=
e
>> 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?
>=20
>  From performance reasons it's pointless to patch. HLT (and MWAIT) are =

> so slow anyways that using patching or an indirect pointer is completel=
y=20
> 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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