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cc7ed3358e
When creating a SPTE, always set the Dirty bit if the Writable bit is set, i.e. if KVM is creating a writable mapping. If two (or more) vCPUs are racing to install a writable SPTE on a !PRESENT fault, only the "winning" vCPU will create a SPTE with W=1 and D=1, all "losers" will generate a SPTE with W=1 && D=0. As a result, tdp_mmu_map_handle_target_level() will fail to detect that the losing faults are effectively spurious, and will overwrite the D=1 SPTE with a D=0 SPTE. For normal VMs, overwriting a present SPTE is a small performance blip; KVM blasts a remote TLB flush, but otherwise life goes on. For upcoming TDX VMs, overwriting a present SPTE is much more costly, and can even lead to the VM being terminated if KVM isn't careful, e.g. if KVM attempts TDH.MEM.PAGE.AUG because the TDX code doesn't detect that the new SPTE is actually the same as the old SPTE (which would be a bug in its own right). Suggested-by: Sagi Shahar <sagis@google.com> Cc: Yan Zhao <yan.y.zhao@intel.com> Link: https://lore.kernel.org/r/20241011021051.1557902-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> |
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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.