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During VMentry VERW is executed to mitigate MDS. After VERW, any memory access like register push onto stack may put host data in MDS affected CPU buffers. A guest can then use MDS to sample host data. Although likelihood of secrets surviving in registers at current VERW callsite is less, but it can't be ruled out. Harden the MDS mitigation by moving the VERW mitigation late in VMentry path. Note that VERW for MMIO Stale Data mitigation is unchanged because of the complexity of per-guest conditional VERW which is not easy to handle that late in asm with no GPRs available. If the CPU is also affected by MDS, VERW is unconditionally executed late in asm regardless of guest having MMIO access. Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Sean Christopherson <seanjc@google.com> Link: https://lore.kernel.org/all/20240213-delay-verw-v8-6-a6216d83edb7%40linux.intel.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.