linux-kernel - Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based private memory

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Message-ID: <Y6B27MpZO8o1Asfe@zn.tnic>
Date:   Mon, 19 Dec 2022 15:36:28 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based
 private memory

On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote:
> In memory encryption usage, guest memory may be encrypted with special
> key and can be accessed only by the guest itself. We call such memory
> private memory. It's valueless and sometimes can cause problem to allow

valueless?

I can't parse that.

> userspace to access guest private memory. This new KVM memslot extension
> allows guest private memory being provided through a restrictedmem
> backed file descriptor(fd) and userspace is restricted to access the
> bookmarked memory in the fd.

bookmarked?

> This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two
> additional KVM memslot fields restricted_fd/restricted_offset to allow
> userspace to instruct KVM to provide guest memory through restricted_fd.
> 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd
> and the size is 'memory_size'.
> 
> The extended memslot can still have the userspace_addr(hva). When use, a

"When un use, ..."

...

> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index a8e379a3afee..690cb21010e7 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -50,6 +50,8 @@ config KVM
>  	select INTERVAL_TREE
>  	select HAVE_KVM_PM_NOTIFIER if PM
>  	select HAVE_KVM_MEMORY_ATTRIBUTES
> +	select HAVE_KVM_RESTRICTED_MEM if X86_64
> +	select RESTRICTEDMEM if HAVE_KVM_RESTRICTED_MEM

Those deps here look weird.

RESTRICTEDMEM should be selected by TDX_GUEST as it can't live without
it.

Then you don't have to select HAVE_KVM_RESTRICTED_MEM simply because of
X86_64 - you need that functionality when the respective guest support
is enabled in KVM.

Then, looking forward into your patchset, I'm not sure you even
need HAVE_KVM_RESTRICTED_MEM - you could make it all depend on
CONFIG_RESTRICTEDMEM. But that's KVM folks call - I'd always aim for
less Kconfig items because we have waay too many.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette