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f2e5b53b4b
Clear R9 in the non-faulting path of KVM_ASM_SAFE() and fall through to to a common load of "vector" to effectively load "vector" with '0' to reduce the code footprint of the asm blob, to reduce the runtime overhead of the non-faulting path (when "vector" is stored in a register), and so that additional output constraints that are valid if and only if a fault occur are loaded even in the non-faulting case. A future patch will add a 64-bit output for the error code, and if its output is not explicitly loaded with _something_, the user of the asm blob can end up technically consuming uninitialized data. Using a common path to load the output constraints will allow using an existing scratch register, e.g. r10, to hold the error code in the faulting path, while also guaranteeing the error code is initialized with deterministic data in the non-faulting patch (r10 is loaded with the RIP of to-be-executed instruction). Consuming the error code when a fault doesn't occur would obviously be a test bug, but there's no guarantee the compiler will detect uninitialized consumption. And conversely, it's theoretically possible that the compiler might throw a false positive on uninitialized data, e.g. if the compiler can't determine that the non-faulting path won't touch the error code. Alternatively, the error code could be explicitly loaded in the non-faulting path, but loading a 64-bit memory|register output operand with an explicitl value requires a sign-extended "MOV imm32, r/m64", which isn't exactly straightforward and has a largish code footprint. And loading the error code with what is effectively garbage (from a scratch register) avoids having to choose an arbitrary value for the non-faulting case. Opportunistically remove a rogue asterisk in the block comment. Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: David Matlack <dmatlack@google.com> Link: https://lore.kernel.org/r/20221102184654.282799-8-dmatlack@google.com |
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| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| 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.