linux-kernel - Re: [RFC PATCH v2 5/5] KVM: Unmap pages only when it's indeed protected for NUMA migration

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Message-ID: <ZNx4OoRQvyh3A0BL@yzhao56-desk.sh.intel.com>
Date:   Wed, 16 Aug 2023 15:18:18 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     bibo mao <maobibo@...ngson.cn>
CC:     Sean Christopherson <seanjc@...gle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <pbonzini@...hat.com>, <mike.kravetz@...cle.com>,
        <apopple@...dia.com>, <jgg@...dia.com>, <rppt@...nel.org>,
        <akpm@...ux-foundation.org>, <kevin.tian@...el.com>,
        <david@...hat.com>
Subject: Re: [RFC PATCH v2 5/5] KVM: Unmap pages only when it's indeed
 protected for NUMA migration

On Wed, Aug 16, 2023 at 03:29:22PM +0800, bibo mao wrote:
> > Flush must be done before kvm->mmu_lock is unlocked, otherwise,
> > confusion will be caused when multiple threads trying to update the
> > secondary MMU.
> Since tlb flush is delayed after all pte entries are cleared, and currently
> there is no tlb flush range supported for secondary mmu. I do know why there
> is confusion before or after kvm->mmu_lock.

Oh, do you mean only do kvm_unmap_gfn_range() in .invalidate_range_end()?
Then check if PROT_NONE is set in primary MMU before unmap?
Looks like a good idea, I need to check if it's feasible.
Thanks!