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64a5d7a109
Extend KVM's suppression of failures due to a userspace access to an
unsupported, but advertised as a "to save" MSR to all MSRs, not just those
that happen to reach the default case statements in kvm_get_msr_common()
and kvm_set_msr_common(). KVM's soon-to-be-established ABI is that if an
MSR is advertised to userspace, then userspace is allowed to read the MSR,
and write back the value that was read, i.e. why an MSR is unsupported
doesn't change KVM's ABI.
Practically speaking, this is very nearly a nop, as the only other paths
that return KVM_MSR_RET_UNSUPPORTED are {svm,vmx}_get_feature_msr(), and
it's unlikely, though not impossible, that userspace is using KVM_GET_MSRS
on unsupported MSRs.
The primary goal of moving the suppression to common code is to allow
returning KVM_MSR_RET_UNSUPPORTED as appropriate throughout KVM, without
having to manually handle the "is userspace accessing an advertised"
waiver. I.e. this will allow formalizing KVM's ABI without incurring a
high maintenance cost.
Link: https://lore.kernel.org/r/20240802181935.292540-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.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 reStructuredText 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.