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Date: Mon, 14 Mar 2022 15:43:46 -0700
From: Isaku Yamahata <isaku.yamahata@...il.com>
To: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
Cc: Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
luto@...nel.org, peterz@...radead.org, x86@...nel.org,
linux-kernel@...r.kernel.org, thomas.lendacky@....com,
brijesh.singh@....com, kirill.shutemov@...ux.intel.com,
hpa@...or.com, pbonzini@...hat.com, seanjc@...gle.com,
srutherford@...gle.com, ashish.kalra@....com,
darren.kenny@...cle.com, venu.busireddy@...cle.com,
boris.ostrovsky@...cle.com, isaku.yamahata@...il.com,
kvm@...r.kernel.org
Subject: Re: [RFC 0/3] Expose Confidential Computing capabilities on sysfs
Added kvm@...r.kernel.org.
On Thu, Mar 10, 2022 at 01:07:33PM -0500,
Alejandro Jimenez <alejandro.j.jimenez@...cle.com> wrote:
>
> On 3/9/2022 5:40 PM, Dave Hansen wrote:
> > On 3/9/22 14:06, Alejandro Jimenez wrote:>
> > > On EPYC Milan host:
> > >
> > > $ grep -r . /sys/kernel/mm/mem_encrypt/*
> > > /sys/kernel/mm/mem_encrypt/c_bit_position:51
> > Why on earth would we want to expose this to userspace?
> >
> > > /sys/kernel/mm/mem_encrypt/sev/nr_sev_asid:509
> > > /sys/kernel/mm/mem_encrypt/sev/status:enabled
> > > /sys/kernel/mm/mem_encrypt/sev/nr_asid_available:509
> > > /sys/kernel/mm/mem_encrypt/sev_es/nr_sev_es_asid:0
> > > /sys/kernel/mm/mem_encrypt/sev_es/status:enabled
> > > /sys/kernel/mm/mem_encrypt/sev_es/nr_asid_available:509
> > > /sys/kernel/mm/mem_encrypt/sme/status:active
> > For all of this... What will userspace *do* with it?
>
> In my case, this information was useful to know for debugging failures when
> testing the various features (e.g. need to specify cbitpos property on QEMU
> sev-guest object).
>
> It helps get an account of what is currently supported/enabled/active on the
> host/guest, given that some of these capabilities will interact with other
> components and cause boot hangs or errors (e.g. AVIC+SME or AVIC+SEV hangs
> at boot, SEV guests with some configurations need to increase SWIOTLB
> limit).
>
> The sysfs entry basically answers the questions in
> https://github.com/AMDESE/AMDSEV#faq without needing to run
> virsh/qmp-shell/rdmsr.
>
> I am aware than having a new sysfs entry mostly to facilitate debugging
> might not be warranted, so I have tagged this as an RFC to ask if others
> working in this space have found additional use cases, or just want the
> convenience of having the data for current and future CoCo features in a
> single location.
> >
> > For nr_asid_available, I get it. It tells you how many guests you can
> > still run. But, TDX will need the same logical thing. Should TDX hosts
> > go looking for this in:
> >
> > /sys/kernel/mm/mem_encrypt/tdx/available_guest_key_ids
> >
> > ?
> >
> > If it's something that's common, it needs to be somewhere common.
> I think it makes sense to have common attributes for all CoCo providers
> under /sys/kernel/mm/mem_encrypt/. The various CoCo providers can create
> entries under mem_encrypt/<feature> exposing the information relevant to
> their specific features like these patches implement for the AMD case, and
> populate or link the <common_attr> attribute with the appropriate value.
>
> Then we can have:
>
> /sys/kernel/mm/mem_encrypt/
> -- common_attr
> -- sme/
> -- sev/
> -- sev_es/
>
> or:
>
> /sys/kernel/mm/mem_encrypt/
> -- common_attr
> -- tdx/
>
> Note that at any single time, we are only creating entries that are
> applicable to the hardware we are running on, so there is not a mix of tdx
> and sme/sev subdirs.
>
> I suspect it will be difficult to agree on what is "common" or even a
> descriptive name. Lets say this common attribute will be:
>
> ?????? ?????? /sys/kernel/mm/mem_encrypt/common_key
>
> Where common_key can represent AMD SEV ASIDs/AMD SEV-{ES,SNP} ASIDs, or
> Intel TDX KeyIDs (private/shared), or s390x SEID (Secure Execution IDs), or
> <insert relevant ARM CCA attribute>.
>
> We can have a (probably long) discussion to agree on the above; this
> patchset just attempts to provide a framework for registering different
> providers, and implements the AMD current capabilities.
The number of available Key IDs (TDX keyid or whatever is called) can be common.
Probably the common misc cgroup is desirable. I don't see other common thing,
though. I don't have requirements to expose bit position etc.
TDX requires firmwares which provide information about themselves. Because
they're firmwares, I'm going to use /sysfs/firmware/tdx.
More concretely
- CPU feature (Secure Arbitration Mode: SEAM) as "seam" flag in /proc/cpuinfo
- TDX firmware(P-SEAMLDR and TDX module) information in /sysfs/firmware/tdx/
What: /sys/firmware/tdx/
Description:
Intel's Trust Domain Extensions (TDX) protect guest VMs from
malicious hosts and some physical attacks. This directory
represents the entry point directory for the TDX.
the TDX requires the TDX firmware to load into an isolated
memory region. It requires a two-step loading process. It uses
the first phase firmware loader (a.k.a NP-SEAMLDR) that loads
the next loader and the second phase firmware loader(a.k.a
P-SEAMLDR) that loads the TDX firmware(a.k.a the "TDX module").
=============== ================================================
keyid_num the number of SEAM keyid as an hexadecimal
number with the "0x" prefix.
=============== ================================================
Users: libvirt
What: /sys/firmware/tdx/p_seamldr/
Description:
The P-SEAMLDR is the TDX module loader. The P-SEAMLDR comes
with its attributes, vendor_id, build_date, build_num, minor
version, major version to identify itself.
Provides the information about the P-SEAMLDR loaded on the
platform. This directory exists if the P-SEAMLDR is
successfully loaded. It contains the following read-only files.
The information corresponds to the data structure, SEAMLDR_INFO.
The admins or VMM management software like libvirt can refer to
that information, determine if P-SEAMLDR is supported, and
identify the loaded P-SEAMLDR.
=============== ================================================
version structure version of SEAMLDR_INFO as an
hexadecimal number with the "0x" prefix
"0x0".
attributes 32bit flags as a hexadecimal number with the
"0x" prefix.
Bit 31 - Production-worthy (0) or
debug (1).
Bits 30:0 - Reserved 0.
vendor_id Vendor ID as a hexadecimal number with the "0x"
prefix.
"0x0806" (Intel P-SEAMLDR module).
build_date Build date in yyyy.mm.dd BCD format.
build_num Build number as a hexadecimal number with the
"0x" prefix.
minor Minor version number as a hexadecimal number
with the "0x" prefix.
major Major version number as a hexadecimal number
with the "0x" prefix.
seaminfo The SEAM information of the TDX module currently
loaded as binary file.
seam_ready A boolean flag that indicates that a debuggable
TDX module can be loaded as a hexadecimal number
with the "0x" prefix.
p_seamldr_ready A boolean flag that indicates that the P-SEAMLDR
module is ready for SEAMCALLs as a hexadecimal
number with the "0x" prefix.
=============== ================================================
Users: libvirt
What: /sys/firmware/tdx/tdx_module/
Description:
The TDX requires a firmware as known as the TDX module. It comes
with its attributes, vendor_id, build_data, build_num,
minor_version, major_version, etc.
Provides the information about the TDX module loaded on the
platform. It contains the following read-only files. The
information corresponds to the data structure, TDSYSINFO_STRUCT.
The admins or VMM management software like libvirt can refer to
that information, determine if TDX is supported, and identify
the loaded the TDX module.
================== ============================================
status string of the TDX module status.
"unknown"
"none": the TDX module is not loaded
"loaded": The TDX module is loaded, but not
initialized
"initialized": the TDX module is fully
initialized
"shutdown": the TDX module is shutdown due to
error during initialization.
attributes 32bit flags of the TDX module attributes as
a hexadecimal number with the "0x" prefix.
Bits 31 - a production module(0) or
a debug module(1).
Bits 30:0 Reserved - set to 0.
vendor_id vendor ID as a hexadecimal number with the
"0x" prefix.
build_date build date in yyyymmdd BCD format.
build_num build number as a hexadecimal number with
the "0x" prefix.
minor_version minor version as a hexadecimal number with
the "0x" prefix.
major_version major versionas a hexadecimal number with
the "0x" prefix.
attributes_fixed0 fixed-0 value for TD's attributes as a
hexadecimal number with the "0x" prefix.
attributes_fixed1 fixed-1 value for TD's attributes as a
hexadecimal number with the "0x" prefix.
xfam_fixed0 fixed-0 value for TD xfam value as a
hexadecimal number with the "0x" prefix.
xfam_fixed1 fixed-1 value for TD xfam value as a
hexadecimal number with the "0x" prefix.
================== =============================================
--
Isaku Yamahata <isaku.yamahata@...il.com>
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