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

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Date:   Tue, 20 Jul 2021 13:23:34 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     brijesh.singh@....com, 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 7/20/21 11:40 AM, Sean Christopherson wrote:
> 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);
> 

Ok.

> 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_*.
> 

ok, I will stick to x86 PG_LEVEL_*

thanks