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Date:   Sun, 13 Nov 2022 16:01:45 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tom Lendacky <thomas.lendacky@....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

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.

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
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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