6bc6f7d9d7
SNP retrieves the majority of CPUID information from the SNP CPUID page.
But there are times when that information needs to be supplemented by the
hypervisor, for example, obtaining the initial APIC ID of the vCPU from
leaf 1.
The current implementation uses the MSR protocol to retrieve the data from
the hypervisor, even when a GHCB exists. The problem arises when an NMI
arrives on return from the VMGEXIT. The NMI will be immediately serviced
and may generate a #VC requiring communication with the hypervisor.
Since a GHCB exists in this case, it will be used. As part of using the
GHCB, the #VC handler will write the GHCB physical address into the GHCB
MSR and the #VC will be handled.
When the NMI completes, processing resumes at the site of the VMGEXIT
which is expecting to read the GHCB MSR and find a CPUID MSR protocol
response. Since the NMI handling overwrote the GHCB MSR response, the
guest will see an invalid reply from the hypervisor and self-terminate.
Fix this problem by using the GHCB when it is available. Any NMI
received is properly handled because the GHCB contents are copied into
a backup page and restored on NMI exit, thus preserving the active GHCB
request or result.
[ bp: Touchups. ]
Fixes: ee0bfa08a345 ("x86/compressed/64: Add support for SEV-SNP CPUID table in #VC handlers")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/a5856fa1ebe3879de91a8f6298b6bbd901c61881.1690578565.git.thomas.lendacky@amd.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.