[Xen-devel] [PATCH] xen: arm: setup sane EL1 state while building domain 0.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

The address translation functions used while building dom0 rely on certain EL1
state being configured. In particular they are subject to the behaviour of
SCTLR_EL1.M (stage 1 MMU enabled).

The Xen (and Linux) boot protocol require that the kernel be entered with the
MMU disabled but they don't say anything explicitly about exception levels
other than the one which is active when entering the kernels. Arguably the
protocol could be said to apply to all exception levels but in any case we
should cope with this and setup the EL1 state as necessary.

Fu Wei discovered this when booting Xen from grub.efi over UEFI, it's not
clear whether grub or UEFI is responsible for leaving stage 1 MMU enabled.

Reported-by: Fu Wei <fu.wei@xxxxxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Fu Wei <fu.wei@xxxxxxxxxx>
---
Fu Wei, can I add your Tested-by here?
---
 xen/arch/arm/domain_build.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 5ca2f15..ea47af5 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -1022,6 +1022,13 @@ int construct_dom0(struct domain *d)
 
     /* The following loads use the domain's p2m */
     p2m_load_VTTBR(d);
+    /* Various EL2 operations, such as guest address translations used
+     * part of the domain build, rely on EL1 state (i.e. whether the
+     * guest has paging enabled). Since the bootloader may have left
+     * this state in an arbitrary configuration set it to something
+     * safe here.
+     */
+    WRITE_SYSREG32(SCTLR_GUEST_INIT, SCTLR_EL1);
 #ifdef CONFIG_ARM_64
     d->arch.type = kinfo.type;
     if ( is_pv32_domain(d) )
-- 
1.7.10.4


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