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908b7d43c0
Skip the MMU permission_fault() check if paging is disabled when verifying the cached MMIO GVA is usable. The check is unnecessary and can theoretically get a false positive since the MMU doesn't zero out "permissions" or "pkru_mask" when guest paging is disabled. The obvious alternative is to zero out all the bitmasks when configuring nonpaging MMUs, but that's unnecessary work and doesn't align with the MMU's general approach of doing as little as possible for flows that are supposed to be unreachable. This is nearly a nop as the false positive is nothing more than an insignificant performance blip, and more or less limited to string MMIO when L1 is running with paging disabled. KVM doesn't cache MMIO if L2 is active with nested TDP since the "GVA" is really an L2 GPA. If L2 is active without nested TDP, then paging can't be disabled as neither VMX nor SVM allows entering the guest without paging of some form. Jumping back to L1 with paging disabled, in that case direct_map is true and so KVM will use CR2 as a GPA; the only time it doesn't is if the fault from the emulator doesn't match or emulator_can_use_gpa(), and that fails only on string MMIO and other instructions with multiple memory operands. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210713163324.627647-27-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.