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474b99ed70
Drop KVM's completely pointless acquisition of mmu_lock when deciding whether or not to unprotect any shadow pages residing at the gfn before resuming the guest to let it retry an instruction that KVM failed to emulated. In this case, indirect_shadow_pages is used as a coarse-grained heuristic to check if there is any chance of there being a relevant shadow page to unprotected. But acquiring mmu_lock largely defeats any benefit to the heuristic, as taking mmu_lock for write is likely far more costly to the VM as a whole than unnecessarily walking mmu_page_hash. Furthermore, the current code is already prone to false negatives and false positives, as it drops mmu_lock before checking the flag and unprotecting shadow pages. And as evidenced by the lack of bug reports, neither false positives nor false negatives are problematic. A false positive simply means that KVM will try to unprotect shadow pages that have already been zapped. And a false negative means that KVM will resume the guest without unprotecting the gfn, i.e. if a shadow page was _just_ created, the vCPU will hit the same page fault and do the whole dance all over again, and detect and unprotect the shadow page the second time around (or not, if something else zaps it first). Reported-by: Jim Mattson <jmattson@google.com> Signed-off-by: Mingwei Zhang <mizhang@google.com> [sean: drop READ_ONCE() and comment change, rewrite changelog] Link: https://lore.kernel.org/r/20240203002343.383056-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> |
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| block | ||
| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
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| rust | ||
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| security | ||
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| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
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| 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.