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

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Date:   Wed, 18 Mar 2020 11:28:37 -0400
From:   Peter Xu <peterx@...hat.com>
To:     maobibo <maobibo@...ngson.cn>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        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 4/4] KVM: MIPS: Define arch-specific
 kvm_flush_remote_tlbs()

On Wed, Mar 18, 2020 at 11:03:13AM +0800, maobibo wrote:
> 
> 
> On 02/08/2020 06:35 AM, Peter Xu wrote:
> > Select HAVE_KVM_ARCH_TLB_FLUSH_ALL for MIPS to define its own
> > kvm_flush_remote_tlbs().  It's as simple as calling the
> > flush_shadow_all(kvm) hook.  Then replace all the flush_shadow_all()
> > calls to use this KVM generic API to do TLB flush.
> > 
> > Signed-off-by: Peter Xu <peterx@...hat.com>
> > ---
> >  arch/mips/kvm/Kconfig |  1 +
> >  arch/mips/kvm/mips.c  | 22 ++++++++++------------
> >  2 files changed, 11 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
> > index eac25aef21e0..8a06f660d39e 100644
> > --- a/arch/mips/kvm/Kconfig
> > +++ b/arch/mips/kvm/Kconfig
> > @@ -26,6 +26,7 @@ config KVM
> >  	select KVM_MMIO
> >  	select MMU_NOTIFIER
> >  	select SRCU
> > +	select HAVE_KVM_ARCH_TLB_FLUSH_ALL
> >  	---help---
> >  	  Support for hosting Guest kernels.
> > 
> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > index 1d5e7ffda746..518020b466bf 100644
> > --- a/arch/mips/kvm/mips.c
> > +++ b/arch/mips/kvm/mips.c
> > @@ -194,13 +194,16 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
> >  	return 0;
> >  }
> > 
> > +void kvm_flush_remote_tlbs(struct kvm *kvm)
> > +{
> > +	kvm_mips_callbacks->flush_shadow_all(kvm);
> > +}
> > +
> Hi Peter,

Hi, Bibo,

> 
> Although I do not understand mip VZ fully, however it changes behavior of
> MIPS VZ, since kvm_flush_remote_tlbs is also called in function
> kvm_mmu_notifier_change_pte/kvm_mmu_notifier_invalidate_range_start

I'm not familiar with MIPS either, however... I would start to suspect
MIPS could be problematic with MMU notifiers when cpu_has_guestid is
not set.  If that's the case, then this series might instead fix it.

Thanks,

-- 
Peter Xu