linux-kernel - Re: [PATCH v2 3/6] KVM: x86: make pic setup code look like ioapic setup

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Message-ID: <0d2c9e2d-f1f6-b107-2250-c323f9bc8edc@redhat.com>
Date:   Wed, 4 Jan 2017 10:10:40 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 3/6] KVM: x86: make pic setup code look like ioapic
 setup

Am 03.01.2017 um 17:12 schrieb Paolo Bonzini:
>
>
> On 03/01/2017 14:04, David Hildenbrand wrote:
>> Am 16.12.2016 um 16:10 schrieb Radim Krčmář:
>>> We don't treat kvm->arch.vpic specially anymore, so the setup can look
>>> like ioapic.  This gets a bit more information out of return values.
>>
>> This originally saved us from a race condition as far as I can
>> reconstruct from the commit history. Think the problem was
>> vpic being set but routes not being set up yet.
>>
>> commit 71ba994c94a81c37185ef2fb5190844286ba9aca
>> Author: Paolo Bonzini <pbonzini@...hat.com>
>> Date:   Wed Jul 29 12:31:15 2015 +0200
>>
>>     KVM: x86: clean/fix memory barriers in irqchip_in_kernel
>>
>>     The memory barriers are trying to protect against concurrent RCU-based
>>     interrupt injection, but the IRQ routing table is not valid at the time
>>     kvm->arch.vpic is written.  Fix this by writing kvm->arch.vpic last.
>>     kvm_destroy_pic then need not set kvm->arch.vpic to NULL; modify it
>>     to take a struct kvm_pic* and reuse it if the IOAPIC creation fails.
>>
>>     Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>
>> I assume that this is now fixed via the irqchip_mode, as it is stored
>> last? If so, I really like this patch :)
>
> Yes, the previous patch referred to that when it said
> "irqchip_in_kernel() tried to save a bit by reusing pic_irqchip()", and
> what this commit message means by "not trteating kvm->arch.vpic
> specially anymore".

Thanks for confirming!

Reviewed-by: David Hildenbrand <david@...hat.com>

>
> Paolo
>


-- 

David