linux-kernel - Re: [PATCH RFC 0/4] KVM: MIPS: Provide arch-specific kvm_flush_remote

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Message-ID: <2db8490e-e4a0-79d0-5088-a9571b01703d@redhat.com>
Date:   Tue, 17 Mar 2020 14:33:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-mips@...r.kernel.org, Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH RFC 0/4] KVM: MIPS: Provide arch-specific
 kvm_flush_remote_tlbs()

On 11/03/20 19:32, Peter Xu wrote:
> On Wed, Feb 12, 2020 at 01:25:30PM +0100, Paolo Bonzini wrote:
>> On 07/02/20 23:35, Peter Xu wrote:
>>> [This series is RFC because I don't have MIPS to compile and test]
>>>
>>> kvm_flush_remote_tlbs() can be arch-specific, by either:
>>>
>>> - Completely replace kvm_flush_remote_tlbs(), like ARM, who is the
>>>   only user of CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL so far
>>>
>>> - Doing something extra before kvm_flush_remote_tlbs(), like MIPS VZ
>>>   support, however still wants to have the common tlb flush to be part
>>>   of the process.  Could refer to kvm_vz_flush_shadow_all().  Then in
>>>   MIPS it's awkward to flush remote TLBs: we'll need to call the mips
>>>   hooks.
>>>
>>> It's awkward to have different ways to specialize this procedure,
>>> especially MIPS cannot use the genenal interface which is quite a
>>> pity.  It's good to make it a common interface.
>>>
>>> This patch series removes the 2nd MIPS usage above, and let it also
>>> use the common kvm_flush_remote_tlbs() interface.  It should be
>>> suggested that we always keep kvm_flush_remote_tlbs() be a common
>>> entrance for tlb flushing on all archs.
>>>
>>> This idea comes from the reading of Sean's patchset on dynamic memslot
>>> allocation, where a new dirty log specific hook is added for flushing
>>> TLBs only for the MIPS code [1].  With this patchset, logically the
>>> new hook in that patch can be dropped so we can directly use
>>> kvm_flush_remote_tlbs().
>>>
>>> TODO: We can even extend another common interface for ranged TLB, but
>>> let's see how we think about this series first.
>>>
>>> Any comment is welcomed, thanks.
>>>
>>> Peter Xu (4):
>>>   KVM: Provide kvm_flush_remote_tlbs_common()
>>>   KVM: MIPS: Drop flush_shadow_memslot() callback
>>>   KVM: MIPS: Replace all the kvm_flush_remote_tlbs() references
>>>   KVM: MIPS: Define arch-specific kvm_flush_remote_tlbs()
>>>
>>>  arch/mips/include/asm/kvm_host.h |  7 -------
>>>  arch/mips/kvm/Kconfig            |  1 +
>>>  arch/mips/kvm/mips.c             | 22 ++++++++++------------
>>>  arch/mips/kvm/trap_emul.c        | 15 +--------------
>>>  arch/mips/kvm/vz.c               | 14 ++------------
>>>  include/linux/kvm_host.h         |  1 +
>>>  virt/kvm/kvm_main.c              | 10 ++++++++--
>>>  7 files changed, 23 insertions(+), 47 deletions(-)
>>>
>>
>> Compile-tested and queued.
> 
> Just in case it fells through the crach - Paolo, do you still have
> plan to queue this again?

Yes, I wanted to make it compile first though.  I'm undecided between
queuing your series and killing KVM MIPS honestly.

Paolo