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Consider a normal (L1) guest running under the main hypervisor (L0), and then a nested guest (L2) running under the L1 guest which is acting as a nested hypervisor. L0 has page tables to map the address space for L1 providing the translation from L1 real address -> L0 real address; L1 | | (L1 -> L0) | ----> L0 There are also page tables in L1 used to map the address space for L2 providing the translation from L2 real address -> L1 read address. Since the hardware can only walk a single level of page table, we need to maintain in L0 a "shadow_pgtable" for L2 which provides the translation from L2 real address -> L0 real address. Which looks like; L2 L2 | | | (L2 -> L1) | | | ----> L1 | (L2 -> L0) | | | (L1 -> L0) | | | ----> L0 --------> L0 When a page fault occurs while running a nested (L2) guest we need to insert a pte into this "shadow_pgtable" for the L2 -> L0 mapping. To do this we need to: 1. Walk the pgtable in L1 memory to find the L2 -> L1 mapping, and provide a page fault to L1 if this mapping doesn't exist. 2. Use our L1 -> L0 pgtable to convert this L1 address to an L0 address, or try to insert a pte for that mapping if it doesn't exist. 3. Now we have a L2 -> L0 mapping, insert this into our shadow_pgtable Once this mapping exists we can take rc faults when hardware is unable to automatically set the reference and change bits in the pte. On these we need to: 1. Check the rc bits on the L2 -> L1 pte match, and otherwise reflect the fault down to L1. 2. Set the rc bits in the L1 -> L0 pte which corresponds to the same host page. 3. Set the rc bits in the L2 -> L0 pte. As we reuse a large number of functions in book3s_64_mmu_radix.c for this we also needed to refactor a number of these functions to take an lpid parameter so that the correct lpid is used for tlb invalidations. The functionality however has remained the same. Reviewed-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com> Signed-off-by: Paul Mackerras <paulus@ozlabs.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.