Hi Vishal,
On 9/14/21 2:00 PM, Vishal Annapurve wrote:
Hi Min, Brijesh,
Regarding:
diff --git a/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
b/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
...
+%ifdef ARCH_IA32
nop
nop
jmp EarlyBspInitReal16
+%else
+
+ smsw ax
We are having intermittent VM crashes with running this code in AMD-SEV
enabled VMs. As per the AMD64 manual
<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24593.pdf&data=04%7C01%7Cbrijesh.singh%40amd.com%7C652023e953924957972a08d977b2031a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637672430875783281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=VFiIbcV6H4xx5XZd%2F0OZjerSfJwLfUjK7mPU9JHY05E%3D&reserved=0> section
15.8.1, executing "smsw" instruction doesn't result in bit 63 being set
in EXITINFO1 and KVM ends up emulating "smsw" instruction by trying to
read encrypted guest VM memory as per the code
<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Fvirt%2Fkvm%2Fkvm.git%2Ftree%2Farch%2Fx86%2Fkvm%2Fsvm%2Fsvm.c%23n2495&data=04%7C01%7Cbrijesh.singh%40amd.com%7C652023e953924957972a08d977b2031a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637672430875783281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=jSw7PLfXjhB8utM7Dxx2P%2F5M3fqvO3q3DBaFW%2Bu03A8%3D&reserved=0>.
Since KVM tries to make sense of different random cipher texts in
different boots, it seems to intermittently result in visible issues.
The smsw does not provide decode assist, in those cases KVM reads the
guest memory and tries to decode. With encrypted guest, the memory
contains the ciphertext and hypervisor will not be able to decode the
instruction.
But it brings a question to Min, why we are using the smsw ? why cannot
use mov CRx. The smsw was meant for very old processors (286 or 8086
etc) and is used for legacy compatibility. The recommendation is to use
the mov CRx. The mov CRx will provide the decode assist to HV.
I looked at the Intel architecture manual [1] and it also recommends
using the mov CRx. The text from the Intel doc.
SMSW is only useful in operating-system software. However,
it is not a privileged instruction and can be used in
application programs if CR4.UMIP = 0. It is provided for
compatibility with the Intel 286 processor. Programs and
procedures intended to run on IA-32 and Intel 64 processors
beginning with the Intel386 processors should use the
MOV CR instruction to load the machine status word.
[1]
https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf
Is this expected behavior or do we miss some configuration or patches
that are recommended by AMD?
This is expected because the smsw does not provide a decode assist, and
encrypted guest will have issues with it. Lets understand the reason
behind using the smsw.
Regards,
Vishal
On Tue, Sep 14, 2021 at 4:54 PM Brijesh Singh via groups.io
<https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgroups.io%2F&data=04%7C01%7Cbrijesh.singh%40amd.com%7C652023e953924957972a08d977b2031a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637672430875793279%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=%2Br4xRTlrqoERthTLJ2YNQAPrKzYX6fid2Q9WNyKybrw%3D&reserved=0>
<brijesh.singh=amd....@groups.io <mailto:amd....@groups.io>> wrote:
Hi Min,
A quick question below.
On 9/14/21 3:50 AM, Min Xu wrote:
> RFC：
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3429&data=04%7C01%7Cbrijesh.singh%40amd.com%7C2cca2f0a7fb44084da2b08d9775cb220%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637672062275443867%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=4zfuIDvTGDNCt%2BD3u7uUR0n6hHDzv%2FI8NkqoUJhsx8Y%3D&reserved=0
<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3429&data=04%7C01%7Cbrijesh.singh%40amd.com%7C652023e953924957972a08d977b2031a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637672430875793279%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=E5bfIvEeyWTgUqnmllwKgSwxycqhzfNnZ72O0i0UKww%3D&reserved=0>
>
> Intel's Trust Domain Extensions (Intel TDX) refers to an Intel
technology
> that extends Virtual Machines Extensions (VMX) and Multi-Key
Total Memory
> Encryption (MKTME) with a new kind of virutal machines guest called a
> Trust Domain (TD). A TD is desinged to run in a CPU mode that
protects the
> confidentiality of TD memory contents and the TD's CPU state from
other
> software, including the hosting Virtual-Machine Monitor (VMM), unless
> explicitly shared by the TD itself.
>
> Note: Intel TDX is only available on X64, so the Tdx related
changes are
> in X64 path. In IA32 path, there may be null stub to make the build
> success.
>
> This patch includes below major changes.
>
> 1. Definition of BFV & CFV
> Tdx Virtual Firmware (TDVF) includes one Firmware Volume (FV) known
> as the Boot Firmware Volume (BFV). The FV format is defined in the
> UEFI Platform Initialization (PI) spec. BFV includes all TDVF
components
> required during boot.
>
> TDVF also include a configuration firmware volume (CFV) that is
separated
> from the BFV. The reason is because the CFV is measured in RTMR,
while
> the BFV is measured in MRTD.
>
> In practice BFV is the code part of Ovmf image (OVMF_CODE.fd).
CFV is the
> vars part of Ovmf image (OVMF_VARS.fd).
>
> 2. PcdOvmfImageSizeInKb
> PcdOvmfImageSizeInKb indicates the size of Ovmf image. It is used to
> calculate the offset of TdxMetadata in ResetVectorVtf0.asm.
In SEV-SNP v7 series, I implemented the metadata support. I did not see
a need for the PcdOvmfImageSizeInKB. Why do you need it? I think your
calculation below will not work if someone is using the OVMF_CODE.fd
instead of OVMF.fd. Have you tried booting with OVMF_CODE.fd ?
thanks
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#80669): https://edk2.groups.io/g/devel/message/80669
Mute This Topic: https://groups.io/mt/85597386/21656
Group Owner: devel+ow...@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com]
-=-=-=-=-=-=-=-=-=-=-=-
