Re: [Xen-devel] [PATCH] x86/MSI: add mechanism to protect MSI-X table from PV guest accesses

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.02.13 at 17:50, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> This adds two new physdev operations for Dom0 to invoke when resource
> allocation for devices is known to be complete, so that the hypervisor
> can arrange for the respective MMIO ranges to be marked read-only
> before an eventual guest getting such a device assigned even gets
> started, such that it won't be able to set up writable mappings for
> these MMIO ranges before Xen has a chance to protect them.

I should probably mention the alternatives:

1) Brute force scan of the (PV) guest's L1 page tables, locating
eventual mappings of the questionable MMIO pages, and
converting those mappings to R/O ones.

2) Snoop BAR modifications (via xen/arch/x86/traps.c:
guest_io_write(), taking note of which BAR(s) are relevant at the
point where the device gets first detected/reported), perhaps
along with snoops of the PCI_COMMAND_MEMORY bit.

Jan


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