linux-kernel - Re: [PATCH v7 11/14] KVM: Register/unregister the guest private memory regions

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Message-ID: <20220720150706.GB124133@chaop.bj.intel.com>
Date:   Wed, 20 Jul 2022 23:07:06 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     "Gupta, Pankaj" <pankaj.gupta@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
        qemu-devel@...gnu.org, linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 11/14] KVM: Register/unregister the guest private
 memory regions

On Tue, Jul 19, 2022 at 04:23:52PM +0200, Gupta, Pankaj wrote:
> 
> > > > +bool __weak kvm_arch_private_mem_supported(struct kvm *kvm)
> > > > +{
> > > > +	return false;
> > > > +}
> > > 
> > > Does this function has to be overriden by SEV and TDX to support the private
> > > regions?
> > 
> > Yes it should be overridden by architectures which want to support it.
> 
> o.k
> > 
> > > 
> > > > +
> > > >    static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
> > > >    {
> > > >    	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
> > > > @@ -4689,6 +4729,22 @@ static long kvm_vm_ioctl(struct file *filp,
> > > >    		r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
> > > >    		break;
> > > >    	}
> > > > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > > > +	case KVM_MEMORY_ENCRYPT_REG_REGION:
> > > > +	case KVM_MEMORY_ENCRYPT_UNREG_REGION: {
> > > > +		struct kvm_enc_region region;
> > > > +
> > > > +		if (!kvm_arch_private_mem_supported(kvm))
> > > > +			goto arch_vm_ioctl;
> > > > +
> > > > +		r = -EFAULT;
> > > > +		if (copy_from_user(&region, argp, sizeof(region)))
> > > > +			goto out;
> > > > +
> > > > +		r = kvm_vm_ioctl_set_encrypted_region(kvm, ioctl, &region);
> > > 
> > > this is to store private region metadata not only the encrypted region?
> > 
> > Correct.
> 
> Sorry for not being clear, was suggesting name change of this function from:
> "kvm_vm_ioctl_set_encrypted_region" to "kvm_vm_ioctl_set_private_region"

Though I don't have strong reason to change it, I'm fine with this and
this name matches the above kvm_arch_private_mem_supported perfectly.

Thanks,
Chao
> 
> > 
> > > 
> > > Also, seems same ioctl can be used to put other regions (e.g firmware, later
> > > maybe DAX backend etc) into private memory?
> > 
> > Possibly. Depends on what exactly the semantics is. If just want to set
> > those regions as private current code already support that.
> 
> Agree. Sure!
> 
> 
> Thanks,
> Pankaj