linux-kernel - Re: [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates

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Message-ID: <YPb8c5qlZ6JuDR05@google.com>
Date:   Tue, 20 Jul 2021 16:40:19 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 25/40] KVM: SVM: Reclaim the guest pages
 when SEV-SNP VM terminates

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_*.