linux-kernel - Re: [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory tracking

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Message-ID: <20200117045019-mutt-send-email-mst@kernel.org>
Date:   Fri, 17 Jan 2020 04:50:48 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christophe de Dinechin <dinechin@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yan Zhao <yan.y.zhao@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Kevin Kevin <kevin.tian@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Lei Cao <lei.cao@...atus.com>
Subject: Re: [PATCH v3 12/21] KVM: X86: Implement ring-based dirty memory
 tracking

On Thu, Jan 16, 2020 at 11:27:03AM -0500, Peter Xu wrote:
> On Thu, Jan 16, 2020 at 03:38:21AM -0500, Michael S. Tsirkin wrote:
> > On Thu, Jan 09, 2020 at 09:57:20AM -0500, Peter Xu wrote:
> > > +	/* If to map any writable page within dirty ring, fail it */
> > > +	if ((kvm_page_in_dirty_ring(vcpu->kvm, vma->vm_pgoff) ||
> > > +	     kvm_page_in_dirty_ring(vcpu->kvm, vma->vm_pgoff + pages - 1)) &&
> > > +	    vma->vm_flags & VM_WRITE)
> > > +		return -EINVAL;
> > 
> > Worth thinking about other flags. Do we want to force VM_SHARED?
> > Disable VM_EXEC?
> 
> Makes sense to me.  I think it worths a standalone patch since they
> should apply for the whole per-vcpu mmaped regions rather than only
> for the dirty ring buffers.
> 
> (Should include KVM_PIO_PAGE_OFFSET, KVM_COALESCED_MMIO_PAGE_OFFSET,
>  KVM_S390_SIE_PAGE_OFFSET, kvm_run, and this new one)
> 
> Thanks,


I don't think we can change UAPI for existing ones.
Userspace might be setting these by mistake.

> -- 
> Peter Xu