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Date:   Mon, 19 Dec 2022 15:36:28 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
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        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
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        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based
 private memory
Message-ID: <Y6B27MpZO8o1Asfe@zn.tnic>
References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com>
 <20221202061347.1070246-4-chao.p.peng@linux.intel.com>
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In-Reply-To: <20221202061347.1070246-4-chao.p.peng@linux.intel.com>
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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