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Virtualize FLUSH_L1D so that the guest can use the performant L1D flush if one of the many mitigations might require a flush in the guest, e.g. Linux provides an option to flush the L1D when switching mms. Passthrough MSR_IA32_FLUSH_CMD for write when it's supported in hardware and exposed to the guest, i.e. always let the guest write it directly if FLUSH_L1D is fully supported. Forward writes to hardware in host context on the off chance that KVM ends up emulating a WRMSR, or in the really unlikely scenario where userspace wants to force a flush. Restrict these forwarded WRMSRs to the known command out of an abundance of caution. Passing through the MSR means the guest can throw any and all values at hardware, but doing so in host context is arguably a bit more dangerous. Link: https://lkml.kernel.org/r/CALMp9eTt3xzAEoQ038bJQ9LN0ZOXrSWsN7xnNUD%2B0SS%3DWwF7Pg%40mail.gmail.com Link: https://lore.kernel.org/all/20230201132905.549148-2-eesposit@redhat.com Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20230322011440.2195485-6-seanjc@google.com> 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.