linux-kernel - Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Date:   Thu, 23 Feb 2023 12:41:47 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Borislav Petkov <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
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        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
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        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
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Subject: Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted

On 2/23/23 12:26, Dave Hansen wrote:
>> +       if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
>> +               /*
>> +               * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
>> +               * bits, just like normal ioremap():
>> +               */
>> +               if (x86_platform.hyper.is_private_mmio(phys))
>> +                       flags = pgprot_encrypted(flags);
>> +               else
>> +                       flags = pgprot_decrypted(flags);
>> +       }
...
> It does seem a bit odd that there's a new CC_ATTR_GUEST_MEM_ENCRYPT
> check wrapping this whole thing.  I guess the trip through
> pgprot_decrypted() is harmless on normal platforms, though.

Yeah, that's _really_ odd.  Sean, were you trying to optimize away the
indirect call or something?

I would just expect the Hyper-V/vTOM code to leave
x86_platform.hyper.is_private_mmio alone unless
it *knows* the platform has private MMIO *and* CC_ATTR_GUEST_MEM_ENCRYPT.

Is there ever a case where CC_ATTR_GUEST_MEM_ENCRYPT==0 and he
Hyper-V/vTOM code would need to set x86_platform.hyper.is_private_mmio?