mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-04-29 16:25:42 -04:00
b64d740ea7
When A/D bits are not available, KVM uses a software access tracking mechanism, which involves making the SPTEs inaccessible. However, the clear_young() MMU notifier does not flush TLBs. So it is possible that there may still be stale, potentially writable, TLB entries. This is usually fine, but can be problematic when enabling dirty logging, because it currently only does a TLB flush if any SPTEs were modified. But if all SPTEs are in access-tracked state, then there won't be a TLB flush, which means that the guest could still possibly write to memory and not have it reflected in the dirty bitmap. So just unconditionally flush the TLBs when enabling dirty logging. As an alternative, KVM could explicitly check the MMU-Writable bit when write-protecting SPTEs to decide if a flush is needed (instead of checking the Writable bit), but given that a flush almost always happens anyway, so just making it unconditional seems simpler. Signed-off-by: Junaid Shahid <junaids@google.com> Message-Id: <20220810224939.2611160-1-junaids@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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.