From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Thu, 19 Sep 2019 19:39:15 +0000
Subject: Re: [PATCH 10/13] KVM: Provide common implementation for generic dirty log functions
Message-Id: <20190919193915.GC30495@linux.intel.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20190911185038.24341-1-sean.j.christopherson@intel.com>
 <20190911185038.24341-11-sean.j.christopherson@intel.com>
 <20190919002242.GA19503@blackberry>
In-Reply-To: <20190919002242.GA19503@blackberry>
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To: Paul Mackerras <paulus@ozlabs.org>
Cc: James Hogan <jhogan@kernel.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>, Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>, Marc Zyngier <marc.zyngier@arm.com>, David Hildenbrand <david@redhat.com>, Cornelia Huck <cohuck@redhat.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, Wanpeng Li <wanpengli@tencent.com>, Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>, James Morse <james.morse@arm.com>, Julien Thierry <julien.thierry@arm.com>, Suzuki K Pouloze <suzuki.poulose@arm.com>, linux-mips@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org

On Thu, Sep 19, 2019 at 10:22:42AM +1000, Paul Mackerras wrote:
> On Wed, Sep 11, 2019 at 11:50:35AM -0700, Sean Christopherson wrote:
> > Move the implementations of KVM_GET_DIRTY_LOG and KVM_CLEAR_DIRTY_LOG
> > for CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT into common KVM code.
> > The arch specific implemenations are extremely similar, differing
> > only in whether the dirty log needs to be sync'd from hardware (x86)
> > and how the TLBs are flushed.  Add new arch hooks to handle sync
> > and TLB flush; the sync will also be used for non-generic dirty log
> > support in a future patch (s390).
> > 
> > The ulterior motive for providing a common implementation is to
> > eliminate the dependency between arch and common code with respect to
> > the memslot referenced by the dirty log, i.e. to make it obvious in the
> > code that the validity of the memslot is guaranteed, as a future patch
> > will rework memslot handling such that id_to_memslot() can return NULL.
> 
> I notice you add empty definitions of kvm_arch_sync_dirty_log() for
> PPC, both Book E and Book 3S.  Given that PPC doesn't select
> CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT, why is this necessary?

s390 has a non-empty kvm_arch_sync_dirty_log() but doesn't select
CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT.  Patch 11/13 moves s390's call
of kvm_arch_sync_dirty_log() from s390's kvm_vm_ioctl_get_dirty_log() into
the common (but not "generic") kvm_get_dirty_log() so that it's obvious
that kvm_vm_ioctl_get_dirty_log() and kvm_get_dirty_log() are operating on
the same memslot, i.e. aren't independently querying id_to_memslot().

I originally made kvm_arch_sync_dirty_log() opt-in with a __KVM_HAVE_ARCH
macro, but the resulting #ifdeffery felt uglier than having PPC and ARM
provide empty functions.