Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 17 Oct 2022 22:17:45 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Fuad Tabba <tabba@google.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
        linux-doc@vger.kernel.org, qemu-devel@nongnu.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
        Steven Price <steven.price@arm.com>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
        ddutile@redhat.com, dhildenb@redhat.com,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>, mhocko@suse.com,
        Muchun Song <songmuchun@bytedance.com>, wei.w.wang@intel.com
Subject: Re: [PATCH v8 5/8] KVM: Register/unregister the guest private memory
 regions
Message-ID: <Y03UiYYioV+FQIpx@google.com>
References: <20220915142913.2213336-1-chao.p.peng@linux.intel.com>
 <20220915142913.2213336-6-chao.p.peng@linux.intel.com>
 <CA+EHjTxukqBfaN6D+rPOiX83zkGknHEQ16J0k6GQSdL_-e9C6g@mail.gmail.com>
 <20221012023516.GA3218049@chaop.bj.intel.com>
 <CA+EHjTyGyGL+ox81=jdtoHERtHPV=P7wJub=3j7chdijyq-AgA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+EHjTyGyGL+ox81=jdtoHERtHPV=P7wJub=3j7chdijyq-AgA@mail.gmail.com>
Precedence: bulk

On Mon, Oct 17, 2022, Fuad Tabba wrote:
> Hi,
> 
> > > > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > > > +#define KVM_MEM_ATTR_SHARED    0x0001
> > > > +static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> > > > +                                    bool is_private)
> > > > +{
> > >
> > > I wonder if this ioctl should be implemented as an arch-specific
> > > ioctl. In this patch it performs some actions that pKVM might not need
> > > or might want to do differently.
> >
> > I think it's doable. We can provide the mem_attr_array kind thing in
> > common code and let arch code decide to use it or not. Currently
> > mem_attr_array is defined in the struct kvm, if those bytes are
> > unnecessary for pKVM it can even be moved to arch definition, but that
> > also loses the potential code sharing for confidential usages in other
> > non-architectures, e.g. if ARM also supports such usage. Or it can be
> > provided through a different CONFIG_ instead of
> > CONFIG_HAVE_KVM_PRIVATE_MEM.
> 
> This sounds good. Thank you.

I like the idea of a separate Kconfig, e.g. CONFIG_KVM_GENERIC_PRIVATE_MEM or
something.  I highly doubt there will be any non-x86 users for multiple years,
if ever, but it would allow testing the private memory stuff on ARM (and any other
non-x86 arch) without needing full pKVM support and with only minor KVM
modifications, e.g. the x86 support[*] to test UPM without TDX is shaping up to be
trivial.

[*] https://lore.kernel.org/all/Y0mu1FKugNQG5T8K@google.com