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Message-ID: <686b824d-e175-1997-7712-1eeee77ae9cb@amd.com>
Date:   Wed, 16 Nov 2022 10:38:08 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "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>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "hch@...radead.org" <hch@...radead.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "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>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v2 05/12] x86/hyperv: Change vTOM handling to use standard
 coco mechanisms

On 11/13/22 10:01, Michael Kelley (LINUX) wrote:
> From: Tom Lendacky <thomas.lendacky@....com> Sent: Friday, November 11, 2022 10:50 AM
>>
>> On 11/11/22 00:21, Michael Kelley wrote:
> 
> [snip]
> 
>>> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
>>> index 06eb8910..024fbf4 100644
>>> --- a/arch/x86/mm/pat/set_memory.c
>>> +++ b/arch/x86/mm/pat/set_memory.c
>>> @@ -2126,10 +2126,8 @@ static int __set_memory_enc_pgtable(unsigned long
>> addr, int numpages, bool enc)
>>>
>>>    static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
>>>    {
>>> -	if (hv_is_isolation_supported())
>>> -		return hv_set_mem_host_visibility(addr, numpages, !enc);
>>> -
>>> -	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
>>> +	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT) ||
>>> +	    cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
>>
>> This seems kind of strange since CC_ATTR_MEM_ENCRYPT is supposed to mean
>> either HOST or GUEST memory encryption, but then you check for GUEST
>> memory encryption directly. Can your cc_platform_has() support be setup to
>> handle the CC_ATTR_MEM_ENCRYPT attribute in some way?
>>
>> Thanks,
>> Tom
> 
> Current upstream code for Hyper-V guests with vTOM enables only
> CC_ATTR_GUEST_MEM_ENCRYPT.  I had been wary of also enabling
> CC_ATTR_MEM_ENCRYPT because that would enable other code paths that
> Might not be right for the vTOM case.  But looking at it more closely, enabling
> CC_ATTR_MEM_ENCRYPT may work.
> 
> There are two problems with Hyper-V vTOM enabling CC_ATTR_MEM_ENCRYPT,
> but both are fixable:
> 
> 1) The call to mem_encrypt_init() happens a little bit too soon.  Hyper-V is fully
> initialized and hypercalls become possible after start_kernel() calls late_time_init().
> mem_encrypt_init() needs to happen after the call to late_time_init() so that
> marking the swiotlb memory as decrypted can make the hypercalls to sync the
> page state change with the host.   Moving mem_encrypt_init() a few lines later in
> start_kernel() works in my case, but I can't test all the cases that you probably
> have.  This change also has the benefit of removing the call to
> swiotlb_update_mem_attributes() at the end of hyperv_init(), which always
> seemed like a hack.

It seems safe for SME/SEV since mem_encrypt_init() is only updating the 
SWIOTLB attributes at this point. I'll do some quick testing, but you 
might want to verify with TDX folks, too.

> 
> 2)  mem_encrypt_free_decrypted_mem() is mismatched with
> sme_postprocess_startup() in its handling of bss decrypted memory.  The
> decryption is done if sme_me_mask is non-zero, while the re-encryption is
> done if CC_ATTR_MEM_ENCRYPT is true, and those conditions won't be
> equivalent in a Hyper-V vTOM VM if we enable CC_ATTR_MEM_ENCRYPT
> (sme_me_mask is always zero in a Hyper-V vTOM VM).  Changing
> mem_encrypt_free_decrypted_mem() to do re-encryption only if sme_me_mask
> is non-zero solves that problem.  Note that there doesn't seem to be a way for a

Hmmm, yes, this was because of an issue using the cc_platform_has() call 
during identity mapped paging. I think matching them in this case would be 
best, e.g., changing mem_encrypt_free_decrypted_mem() to check for a 
non-zero sme_me_mask - along with a nice comment on why it is checking 
sme_me_mask.

Thanks,
Tom

> Hyper-V vTOM VM to have decrypted bss, since there's no way to sync the
> page state change with the host that early in the boot process, but I don't think
> there's a requirement for such, so all is good.
> 
> With the above two changes, Hyper-V vTOM VMs can enable
> CC_ATTR_MEM_ENCRYPT.  The Hyper-V hack in __set_memory_enc_dec()
> still goes away, and there's no change to the condition for invoking
> __set_memory_enc_pgtable().
> 
> Thoughts?  Have I missed anything?  Overall, I'm persuaded that this is a better
> approach and can submit a v3 patch series with these changes if you agree.
> 
> Michael

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