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Date:   Wed, 19 Oct 2022 21:23:08 +0800
From:   Chao Peng <chao.p.peng@linux.intel.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Fuad Tabba <tabba@google.com>, kvm@vger.kernel.org,
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Subject: Re: [PATCH v8 5/8] KVM: Register/unregister the guest private memory
 regions
Message-ID: <20221019132308.GA3496045@chaop.bj.intel.com>
Reply-To: Chao Peng <chao.p.peng@linux.intel.com>
References: <20220915142913.2213336-1-chao.p.peng@linux.intel.com>
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 <Y03UiYYioV+FQIpx@google.com>
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On Mon, Oct 17, 2022 at 10:17:45PM +0000, Sean Christopherson wrote:
> On Mon, Oct 17, 2022, Fuad Tabba wrote:
> > Hi,
> > 
> > > > > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
> > > > > +#define KVM_MEM_ATTR_SHARED    0x0001
> > > > > +static int kvm_vm_ioctl_set_mem_attr(struct kvm *kvm, gpa_t gpa, gpa_t size,
> > > > > +                                    bool is_private)
> > > > > +{
> > > >
> > > > I wonder if this ioctl should be implemented as an arch-specific
> > > > ioctl. In this patch it performs some actions that pKVM might not need
> > > > or might want to do differently.
> > >
> > > I think it's doable. We can provide the mem_attr_array kind thing in
> > > common code and let arch code decide to use it or not. Currently
> > > mem_attr_array is defined in the struct kvm, if those bytes are
> > > unnecessary for pKVM it can even be moved to arch definition, but that
> > > also loses the potential code sharing for confidential usages in other
> > > non-architectures, e.g. if ARM also supports such usage. Or it can be
> > > provided through a different CONFIG_ instead of
> > > CONFIG_HAVE_KVM_PRIVATE_MEM.
> > 
> > This sounds good. Thank you.
> 
> I like the idea of a separate Kconfig, e.g. CONFIG_KVM_GENERIC_PRIVATE_MEM or
> something.  I highly doubt there will be any non-x86 users for multiple years,
> if ever, but it would allow testing the private memory stuff on ARM (and any other
> non-x86 arch) without needing full pKVM support and with only minor KVM
> modifications, e.g. the x86 support[*] to test UPM without TDX is shaping up to be
> trivial.

CONFIG_KVM_GENERIC_PRIVATE_MEM looks good to me.

Thanks,
Chao
> 
> [*] https://lore.kernel.org/all/Y0mu1FKugNQG5T8K@google.com