docs/pvh: document initial MTRR state

Provided to both Dom0 and DomUs.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

diff --git a/docs/misc/pvh.markdown b/docs/misc/pvh.markdown
index e85fb15374b162ec77eaaaa7e3f940cfcadc9996..1c9a00b48a8bce9f3c15c228cf624efc1c91fd68 100644 (file)
--- a/docs/misc/pvh.markdown
+++ b/docs/misc/pvh.markdown
@@ -92,3 +92,21 @@ event channels. Delivery of those interrupts can be configured in the same way
 as HVM guests, check xen/include/public/hvm/params.h and
 xen/include/public/hvm/hvm\_op.h for more information about available delivery
 methods.
+
+## MTRR ##
+
+### Unprivileged guests ###
+
+PVH guests are currently booted with the default MTRR type set to write-back
+and MTRR enabled. This allows DomUs to start with a sane MTRR state. Note that
+this will have to be revisited when pci-passthrough is added to PVH in order to
+set MMIO regions as UC.
+
+Xen guarantees that RAM regions will always have the WB cache type set in the
+initial MTRR state, either set by the default MTRR type or by other means.
+
+### Hardware domain ###
+
+A PVH hardware domain is booted with the same MTRR state as the one found on
+the host. This is done because the hardware domain memory map is already a
+modified copy of the host memory map, so the same MTRR setup should work.