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[Xen-devel] [PATCH v4 8/8] docs/pvh: document initial MTRR state

Provided to both Dom0 and DomUs.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Changes since v2:
 - Add 'currently' to the first sentence about the default MTRR type.

Changes since v1:
 - Add an extra paragraph to clarify the initial MTRR state.
 docs/misc/pvh.markdown | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/docs/misc/pvh.markdown b/docs/misc/pvh.markdown
index e85fb15374..1c9a00b48a 100644
--- 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
+## 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.

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