linux-kernel - Re: [PATCH 03/13] kvm: monolithic: fixup x86-32 build

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Message-ID: <9a3d2936-bd26-430f-a962-9b0f6fe0c2a0@redhat.com>
Date:   Fri, 8 Nov 2019 22:02:52 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Jessica Yu <jeyu@...nel.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Matthias Maennich <maennich@...gle.com>
Subject: Re: [PATCH 03/13] kvm: monolithic: fixup x86-32 build

On 08/11/19 21:01, Andrea Arcangeli wrote:
> On Fri, Nov 08, 2019 at 08:51:04PM +0100, Paolo Bonzini wrote:
>> I suppose we could use code patching mechanism to avoid the retpolines.
>>  Andrea, what do you think about that?  That would have the advantage
>> that we won't have to remove kvm_x86_ops. :)
> 
> page 17 covers pvops:
> 
> https://people.redhat.com/~aarcange/slides/2019-KVM-monolithic.pdf

You can patch call instructions directly using text_poke when
kvm_intel.ko or kvm_amd.ko, I'm not sure why that would be worse for TLB
or RAM usage.  The hard part is recording the location of the call sites
using some pushsection/popsection magic.

Paolo