860e334395
commit 764643a6be07445308e492a528197044c801b3ba upstream. If a nested run isn't pending, snapshot vmcs01.GUEST_IA32_DEBUGCTL irrespective of whether or not VM_ENTRY_LOAD_DEBUG_CONTROLS is set in vmcs12. When restoring nested state, e.g. after migration, without a nested run pending, prepare_vmcs02() will propagate nested.vmcs01_debugctl to vmcs02, i.e. will load garbage/zeros into vmcs02.GUEST_IA32_DEBUGCTL. If userspace restores nested state before MSRs, then loading garbage is a non-issue as loading DEBUGCTL will also update vmcs02. But if usersepace restores MSRs first, then KVM is responsible for propagating L2's value, which is actually thrown into vmcs01, into vmcs02. Restoring L2 MSRs into vmcs01, i.e. loading all MSRs before nested state is all kinds of bizarre and ideally would not be supported. Sadly, some VMMs do exactly that and rely on KVM to make things work. Note, there's still a lurking SMM bug, as propagating vmcs01's DEBUGCTL to vmcs02 across RSM may corrupt L2's DEBUGCTL. But KVM's entire VMX+SMM emulation is flawed as SMI+RSM should not toouch _any_ VMCS when use the "default treatment of SMIs", i.e. when not using an SMI Transfer Monitor. Link: https://lore.kernel.org/all/Yobt1XwOfb5M6Dfa@google.com Fixes: 8fcc4b5923af ("kvm: nVMX: Introduce KVM_CAP_NESTED_STATE") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20220614215831.3762138-3-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.