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In general, activating long mode involves setting the EFER_LME bit in the EFER register and then enabling the X86_CR0_PG bit in the CR0 register. At this point, the EFER_LMA bit will be set automatically by hardware. In the case of SVM/SEV guests where writes to CR0 are intercepted, it's necessary for the host to set EFER_LMA on behalf of the guest since hardware does not see the actual CR0 write. In the case of SEV-ES guests where writes to CR0 are trapped instead of intercepted, the hardware *does* see/record the write to CR0 before exiting and passing the value on to the host, so as part of enabling SEV-ES support commitf1c6366e30("KVM: SVM: Add required changes to support intercepts under SEV-ES") dropped special handling of the EFER_LMA bit with the understanding that it would be set automatically. However, since the guest never explicitly sets the EFER_LMA bit, the host never becomes aware that it has been set. This becomes problematic when userspace tries to get/set the EFER values via KVM_GET_SREGS/KVM_SET_SREGS, since the EFER contents tracked by the host will be missing the EFER_LMA bit, and when userspace attempts to pass the EFER value back via KVM_SET_SREGS it will fail a sanity check that asserts that EFER_LMA should always be set when X86_CR0_PG and EFER_LME are set. Fix this by always inferring the value of EFER_LMA based on X86_CR0_PG and EFER_LME, regardless of whether or not SEV-ES is enabled. Fixes:f1c6366e30("KVM: SVM: Add required changes to support intercepts under SEV-ES") Reported-by: Peter Gonda <pgonda@google.com> Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210507165947.2502412-2-seanjc@google.com> [A two year old patch that was revived after we noticed the failure in KVM_SET_SREGS and a similar patch was posted by Michael Roth. This is Sean's patch, but with Michael's more complete commit message. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.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.