linux-kernel - Re: [PATCH v3 26/28] KVM: selftests: Split out helper to allocate guest mem via memfd

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Message-ID: <764356ef-dd0f-01bd-129c-a821136a4f6e@redhat.com>
Date:   Wed, 2 Mar 2022 19:36:35 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH v3 26/28] KVM: selftests: Split out helper to allocate
 guest mem via memfd

On 3/1/22 00:36, David Woodhouse wrote:
> On Sat, 2022-02-26 at 00:15 +0000, Sean Christopherson wrote:
>> Extract the code for allocating guest memory via memfd out of
>> vm_userspace_mem_region_add() and into a new helper, kvm_memfd_alloc().
>> A future selftest to populate a guest with the maximum amount of guest
>> memory will abuse KVM's memslots to alias guest memory regions to a
>> single memfd-backed host region, i.e. needs to back a guest with memfd
>> memory without a 1:1 association between a memslot and a memfd instance.
>>
>> No functional change intended.
>>
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> 
> While we're at it, please can we make the whole thing go away and just
> return failure #ifndef MFD_CLOEXEC, instead of breaking the build on
> older userspace?

We can just use old school F_SETFD if that's helpful for you.

Paolo