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9245fd6b85
As a result of a recent investigation, it was determined that x86 CPUs which support 5-level paging, don't always respect CR4.LA57 when doing canonical checks. In particular: 1. MSRs which contain a linear address, allow full 57-bitcanonical address regardless of CR4.LA57 state. For example: MSR_KERNEL_GS_BASE. 2. All hidden segment bases and GDT/IDT bases also behave like MSRs. This means that full 57-bit canonical address can be loaded to them regardless of CR4.LA57, both using MSRS (e.g GS_BASE) and instructions (e.g LGDT). 3. TLB invalidation instructions also allow the user to use full 57-bit address regardless of the CR4.LA57. Finally, it must be noted that the CPU doesn't prevent the user from disabling 5-level paging, even when the full 57-bit canonical address is present in one of the registers mentioned above (e.g GDT base). In fact, this can happen without any userspace help, when the CPU enters SMM mode - some MSRs, for example MSR_KERNEL_GS_BASE are left to contain a non-canonical address in regard to the new mode. Since most of the affected MSRs and all segment bases can be read and written freely by the guest without any KVM intervention, this patch makes the emulator closely follow hardware behavior, which means that the emulator doesn't take in the account the guest CPUID support for 5-level paging, and only takes in the account the host CPU support. Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> Link: https://lore.kernel.org/r/20240906221824.491834-4-mlevitsk@redhat.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.