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4286a3ec25
Add support for "fast" aging of SPTEs in both the TDP MMU and Shadow MMU, where "fast" means "without holding mmu_lock". Not taking mmu_lock allows multiple aging actions to run in parallel, and more importantly avoids stalling vCPUs, e.g. due to holding mmu_lock for an extended duration while a vCPU is faulting in memory. For the TDP MMU, protect aging via RCU; the page tables are RCU-protected and KVM doesn't need to access any metadata to age SPTEs. For the Shadow MMU, use bit 1 of rmap pointers (bit 0 is used to terminate a list of rmaps) to implement a per-rmap single-bit spinlock. When aging a gfn, acquire the rmap's spinlock with read-only permissions, which allows hardening and optimizing the locking and aging, e.g. locking an rmap for write requires mmu_lock to also be held. The lock is NOT a true R/W spinlock, i.e. multiple concurrent readers aren't supported. To avoid forcing all SPTE updates to use atomic operations (clearing the Accessed bit out of mmu_lock makes it inherently volatile), rework and rename spte_has_volatile_bits() to spte_needs_atomic_update() and deliberately exclude the Accessed bit. KVM (and mm/) already tolerates false positives/negatives for Accessed information, and all testing has shown that reducing the latency of aging is far more beneficial to overall system performance than providing "perfect" young/old information. -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEKTobbabEP7vbhhN9OlYIJqCjN/0FAmfZizUACgkQOlYIJqCj N/1XkBAAwLxK3uKwkIIgzu+V6NPMiqPBsNtGiiQgRYMfvCwMW2vU6ztsBgNgs6zI eMnOCCo6fQaxPFvpKue8VN7TD33BcjzKZaPiuHZrzQIa/oYQeOlZ4oaN8lr9F9Ec 5l1Lg/p2+z1GGDhWc2opNpg48sCtX7IQ0Tx46LkoB3VSDFP33GwW4+Ht2r71rNeL ofKB+T0hU5HOry5j0w0nTVwOEoNzlm1sVFqOHzgnK18Lmqw2CfOPm+46K+w8nOh+ v+rwGuGa//1kcCjNCcGP1OuJdNAMgXBxND/l6LAkWcHfffIRbXlO07O05dAGqPeF rRn5JUl02OkI6lq99+935OmtEROe6mt+Bx0dhAzk4Z0CD6JY34ShZSAADSnltQlK 2a1E95t63v8a7ZM5dwED7os2HBhxODoyeWQAlIHpkVdmeTJstkyvjPhubJc13+Js oDL6ehs3hhZ171ePn2aXo0NobA5fe7xbl4wugP3hNmBXjLvu04D+llcDmC095nBk ICuzFqFXCXzdjEwgWwPzTseWOCoWTkoRqeJ9lch4UD3mMMcmK0MbK6joocGvCFto cL/eZdElnf1MZwWYdo44X+NEc1jItZVvktkRrllpwCtpRSDINO6RYZGcRf/g0Lha XmaU7jICfi3AKc4N3S2l4KIkd/AeJQySM+kGArxIOYoaqFCe2Mc= =Iy57 -----END PGP SIGNATURE----- Merge tag 'kvm-x86-mmu-6.15' of https://github.com/kvm-x86/linux into HEAD KVM x86/mmu changes for 6.15 Add support for "fast" aging of SPTEs in both the TDP MMU and Shadow MMU, where "fast" means "without holding mmu_lock". Not taking mmu_lock allows multiple aging actions to run in parallel, and more importantly avoids stalling vCPUs, e.g. due to holding mmu_lock for an extended duration while a vCPU is faulting in memory. For the TDP MMU, protect aging via RCU; the page tables are RCU-protected and KVM doesn't need to access any metadata to age SPTEs. For the Shadow MMU, use bit 1 of rmap pointers (bit 0 is used to terminate a list of rmaps) to implement a per-rmap single-bit spinlock. When aging a gfn, acquire the rmap's spinlock with read-only permissions, which allows hardening and optimizing the locking and aging, e.g. locking an rmap for write requires mmu_lock to also be held. The lock is NOT a true R/W spinlock, i.e. multiple concurrent readers aren't supported. To avoid forcing all SPTE updates to use atomic operations (clearing the Accessed bit out of mmu_lock makes it inherently volatile), rework and rename spte_has_volatile_bits() to spte_needs_atomic_update() and deliberately exclude the Accessed bit. KVM (and mm/) already tolerates false positives/negatives for Accessed information, and all testing has shown that reducing the latency of aging is far more beneficial to overall system performance than providing "perfect" young/old information. |
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| arch | ||
| block | ||
| 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 | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| MAINTAINERS | ||
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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 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.