Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 20 Jul 2021 16:40:19 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Brijesh Singh <brijesh.singh@amd.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>, tony.luck@intel.com,
        npmccallum@redhat.com, brijesh.ksingh@gmail.com
Subject: Re: [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages
 when SEV-SNP VM terminates
Message-ID: <YPb8c5qlZ6JuDR05@google.com>
References: <20210707183616.5620-1-brijesh.singh@amd.com>
 <20210707183616.5620-26-brijesh.singh@amd.com>
 <YPHnb5pW9IoTcwWU@google.com>
 <2711d9f9-21a0-7baa-d0ff-2c0f69ca6949@amd.com>
 <YPIoaoDCjNVzn2ZM@google.com>
 <e1cc1e21-e7b7-5930-1c01-8f4bb6e43b3a@amd.com>
 <YPWz6YwjDZcla5/+@google.com>
 <912c929c-06ba-a391-36bb-050384907d81@amd.com>
 <YPXMas+9O1Y5910b@google.com>
 <96154428-4c18-9e5f-3742-d0446a8d9848@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <96154428-4c18-9e5f-3742-d0446a8d9848@amd.com>
Precedence: bulk

On Mon, Jul 19, 2021, Brijesh Singh wrote:
> 
> On 7/19/21 2:03 PM, Sean Christopherson wrote:
> > On Mon, Jul 19, 2021, Brijesh Singh wrote:
> > Ah, not firmwrare, gotcha.  But we can still use a helper, e.g. an inner
> > double-underscore helper, __rmp_make_private().
> 
> In that case we are basically passing the all the fields defined in the
> 'struct rmpupdate' as individual arguments.

Yes, but (a) not _all_ fields, (b) it would allow hiding "struct rmpupdate", and
(c) this is much friendlier to readers:

	__rmp_make_private(pfn, gpa, PG_LEVEL_4K, svm->asid, true);

than:

	rmpupdate(&rmpupdate);

For the former, I can see in a single line of code that KVM is creating a 4k
private, immutable guest page.  With the latter, I need to go hunt down all code
that modifies rmpupdate to understand what the code is doing.

> How about something like this:
> 
> * core kernel exports the rmpupdate()
> * the include/linux/sev.h header file defines the helper functions
> 
>   int rmp_make_private(u64 pfn, u64 gpa, int psize, int asid)

I think we'll want s/psize/level, i.e. make it more obvious clear that the input
is PG_LEVEL_*.