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

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Message-ID: <20200207230015.GI720553@xz-x1>
Date:   Fri, 7 Feb 2020 18:00:15 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.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 Fri, Feb 07, 2020 at 05:35:16PM -0500, 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

[1] https://lore.kernel.org/kvm/20200207194532.GK2401@linux.intel.com/T/#m2da733d75dab5e54e2ae68de94fe8411166d6274

> 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(-)
> 
> -- 
> 2.24.1
> 

-- 
Peter Xu