cf1d88b36b
It isn't OK to cache the dirty status of a page in internal structures for an indefinite period of time. Any time a vCPU exits the run loop to userspace might be its last; the VMM might do its final check of the dirty log, flush the last remaining dirty pages to the destination and complete a live migration. If we have internal 'dirty' state which doesn't get flushed until the vCPU is finally destroyed on the source after migration is complete, then we have lost data because that will escape the final copy. This problem already exists with the use of kvm_vcpu_unmap() to mark pages dirty in e.g. VMX nesting. Note that the actual Linux MM already considers the page to be dirty since we have a writeable mapping of it. This is just about the KVM dirty logging. For the nesting-style use cases (KVM_GUEST_USES_PFN) we will need to track which gfn_to_pfn_caches have been used and explicitly mark the corresponding pages dirty before returning to userspace. But we would have needed external tracking of that anyway, rather than walking the full list of GPCs to find those belonging to this vCPU which are dirty. So let's rely *solely* on that external tracking, and keep it simple rather than laying a tempting trap for callers to fall into. Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20220303154127.202856-3-dwmw2@infradead.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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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.