linux-kernel - Re: [RFC 02/16] KVM: selftests: add hooks for managing encrypted guest memory

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Date:   Wed, 20 Oct 2021 22:37:23 -0500
From:   Michael Roth <michael.roth@....com>
To:     Mingwei Zhang <mizhang@...gle.com>
CC:     <linux-kselftest@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Nathan Tempelman <natet@...gle.com>,
        Marc Orr <marcorr@...gle.com>,
        Steve Rutherford <srutherford@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Brijesh Singh" <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Varad Gautam" <varad.gautam@...e.com>,
        Shuah Khan <shuah@...nel.org>,
        "Vitaly Kuznetsov" <vkuznets@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "Ricardo Koller" <ricarkol@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC 02/16] KVM: selftests: add hooks for managing encrypted
 guest memory

On Mon, Oct 18, 2021 at 08:00:00AM -0700, Mingwei Zhang wrote:
> > +void vm_set_memory_encryption(struct kvm_vm *vm, bool enc_by_default, bool has_enc_bit,
> > +                             uint8_t enc_bit)
> > +{
> > +       vm->memcrypt.enabled = true;
> > +       vm->memcrypt.enc_by_default = enc_by_default;
> > +       vm->memcrypt.has_enc_bit = has_enc_bit;
> > +       vm->memcrypt.enc_bit = enc_bit;
> > +}
> > +
> > +struct sparsebit *
> > +vm_get_encrypted_phy_pages(struct kvm_vm *vm, int slot, vm_paddr_t *gpa_start,
> > +                          uint64_t *size)
> > +{
> > +       struct userspace_mem_region *region;
> > +       struct sparsebit *encrypted_phy_pages;
> > +
> > +       if (!vm->memcrypt.enabled)
> > +               return NULL;
> > +
> > +       region = memslot2region(vm, slot);
> > +       if (!region)
> > +               return NULL;
> > +
> > +       encrypted_phy_pages = sparsebit_alloc();
> > +       sparsebit_copy(encrypted_phy_pages, region->encrypted_phy_pages);
> 
> Do we have to make a copy for the sparsebit? Why not just return the
> pointer? By looking at your subsequent patches, I find that this data
> structure seems to be just read-only?

Yes, it's only intended to be used for read access. But I'll if I can
enforce that without the need to use a copy.

> 
> -Mingwei