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

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Message-ID: <20221221134246.GB1766136@chaop.bj.intel.com>
Date:   Wed, 21 Dec 2022 21:42:46 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
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>,
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        wei.w.wang@...el.com
Subject: Re: [PATCH v10 3/9] KVM: Extend the memslot to support fd-based
 private memory

On Tue, Dec 20, 2022 at 10:55:44AM +0100, Borislav Petkov wrote:
> On Tue, Dec 20, 2022 at 03:43:18PM +0800, Chao Peng wrote:
> > RESTRICTEDMEM is needed by TDX_HOST, not TDX_GUEST.
> 
> Which basically means that RESTRICTEDMEM should simply depend on KVM.
> Because you can't know upfront whether KVM will run a TDX guest or a SNP
> guest and so on.
> 
> Which then means that RESTRICTEDMEM will practically end up always
> enabled in KVM HV configs.

That's right, CONFIG_RESTRICTEDMEM is always selected for supported KVM
architectures (currently x86_64).

> 
> > The only reason to add another HAVE_KVM_RESTRICTED_MEM is some code only
> > works for 64bit[*] and CONFIG_RESTRICTEDMEM is not sufficient to enforce
> > that.
> 
> This is what I mean with "we have too many Kconfig items". :-\

Yes I agree. One way to remove this is probably additionally checking
CONFIG_64BIT instead.

Thanks,
Chao
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette