Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
4af7715110
When shadow paging is enabled, KVM tracks the allowed access type for
MMIO SPTEs so that it can do a permission check on a MMIO GVA cache hit
without having to walk the guest's page tables. The tracking is done
by retaining the WRITE and USER bits of the access when inserting the
MMIO SPTE (read access is implicitly allowed), which allows the MMIO
page fault handler to retrieve and cache the WRITE/USER bits from the
SPTE.
Unfortunately for EPT, the mask used to retain the WRITE/USER bits is
hardcoded using the x86 paging versions of the bits. This funkiness
happens to work because KVM uses a completely different mask/value for
MMIO SPTEs when EPT is enabled, and the EPT mask/value just happens to
overlap exactly with the x86 WRITE/USER bits[*].
Explicitly define the access mask for MMIO SPTEs to accurately reflect
that EPT does not want to incorporate any access bits into the SPTE, and
so that KVM isn't subtly relying on EPT's WX bits always being set in
MMIO SPTEs, e.g. attempting to use other bits for experimentation breaks
horribly.
Note, vcpu_match_mmio_gva() explicits prevents matching GVA==0, and all
TDP flows explicit set mmio_gva to 0, i.e. zeroing vcpu->arch.access for
EPT has no (known) functional impact.
[*] Using WX to generate EPT misconfigurations (equivalent to reserved
bit page fault) ensures KVM can employ its MMIO page fault tricks
even platforms without reserved address bits.
Fixes:
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||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| 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 | ||
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.