linux-kernel - Re: [PATCH 1/1] x86/apic: Introduce paravirq irq

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Message-ID: <5aaeb0ec-fd16-ab28-3892-3c6a18165a30@linux.com>
Date:	Thu, 18 Aug 2016 01:58:51 +0300
From:	Alexander Popov <alex.popov@...ux.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Marc Zyngier <marc.zyngier@....com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Jason Cooper <jason@...edaemon.net>,
	Radim Krcmar <rkrcmar@...hat.com>,
	Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/apic: Introduce paravirq irq_domain

On 17.08.2016 17:36, Jan Kiszka wrote:
> On 2016-08-15 14:37, Paolo Bonzini wrote:
>> On 15/08/2016 13:51, Alexander Popov wrote:
>>> It seems to me that the idea of an irq_domain for interrupts injected
>>> by a hypervisor is quite generic.
>>
>> True, but all of Xen, KVM and VMware use PCI devices for this.
> 
> So does Jailhouse. We have to have the code anyway because we need to
> keep Linux alive after taking over control. Thus it is actually easier
> to reuse the same logic for para-virtualized domains (non-root cells).

Hello, Jan! Yes, I see.

I can only say that Xen, KVM, VMware and Jailhouse happily use hypercalls,
which are a valid interface between a hypervisor and its guests.

Positive Technologies hypervisor called Gvandra (named after a big Caucasus
mountain) tries to use only the hypercalls and avoid PCI device emulation
to become slimmer.

Best regards,
Alexander