linux-kernel - Re: [PATCH v2 00/30] KVM: s390: enable zPCI for interpretive execution

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Message-ID: <5c84960c-1075-02e1-b342-6e0c1abaa46e@linux.ibm.com>
Date:   Wed, 19 Jan 2022 19:10:47 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        vneethv@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/30] KVM: s390: enable zPCI for interpretive
 execution



On 1/14/22 21:31, Matthew Rosato wrote:
> Enable interpretive execution of zPCI instructions + adapter interruption
> forwarding for s390x KVM vfio-pci.  This is done by introducing a series
> of new vfio-pci feature ioctls that are unique vfio-pci-zdev (s390x) and
> are used to negotiate the various aspects of zPCI interpretation setup.
> By allowing intepretation of zPCI instructions and firmware delivery of
> interrupts to guests, we can significantly reduce the frequency of guest
> SIE exits for zPCI.  We then see additional gains by handling a hot-path
> instruction that can still intercept to the hypervisor (RPCIT) directly
> in kvm.
> 
>  From the perspective of guest configuration, you passthrough zPCI devices
> in the same manner as before, with intepretation support being used by
> default if available in kernel+qemu.
> 
> Will reply with a link to the associated QEMU series.

I did the comment in a patch but I think that centralizing it here is 
clearer: I think having a documentation in Documentation/S390 like we 
have already for VFIO AP and VFIO CCW would be a good thing.

-- 
Pierre Morel
IBM Lab Boeblingen