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: <96154428-4c18-9e5f-3742-d0446a8d9848@amd.com>
Date:   Mon, 19 Jul 2021 14:37:06 -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 7/19/21 2:03 PM, Sean Christopherson wrote:
> On Mon, Jul 19, 2021, Brijesh Singh wrote:
>>
>> On 7/19/21 12:18 PM, Sean Christopherson wrote:
>>>>
>>>> Okay, I will add helper to make things easier. One case where we will
>>>> need to directly call the rmpupdate() is during the LAUNCH_UPDATE
>>>> command. In that case the page is private and its immutable bit is also
>>>> set. This is because the firmware makes change to the page, and we are
>>>> required to set the immutable bit before the call.
>>>
>>> Or do "int rmp_make_firmware(u64 pfn, bool immutable)"?
>>
>> That's not what we need.
>>
>> We need 'rmp_make_private() + immutable' all in one RMPUPDATE.  Here is the
>> snippet from SNP_LAUNCH_UPDATE.
> 
> 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. 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)
   int rmp_make_firmware(u64 pfn, int psize);
   int rmp_make_shared(u64 pfn, int psize);

In most of the case above 3 helpers are good. If driver finds that the 
above helper does not fit its need (such as SNP_LAUNCH_UPDATE) then call 
the rmpupdate() without going through the helper.

-Brijesh