[RFC PATCH] xen/arm: p2m don't fall over on FEAT_LPA enabled hw

[Alex Bennée <alex.bennee@xxxxxxxxxx>]

When we introduced FEAT_LPA to QEMU's -cpu max we discovered older
kernels had a bug where the physical address was copied directly from
ID_AA64MMFR0_EL1.PARange field. The early cpu_init code of Xen commits
the same error by blindly copying across the max supported range.

Unsurprisingly when the page tables aren't set up for these greater
ranges hilarity ensues and the hypervisor crashes fairly early on in
the boot-up sequence. This happens when we write to the control
register in enable_mmu().

Attempt to fix this the same way as the Linux kernel does by gating
PARange to the maximum the hypervisor can handle. I also had to fix up
code in p2m which panics when it sees an "invalid" entry in PARange.

Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
Cc: Richard Henderson <richard.henderson@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
Cc: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---
 xen/arch/arm/arm64/head.S | 6 ++++++
 xen/arch/arm/p2m.c        | 9 ++++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index aa1f88c764..057dd5d925 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -473,6 +473,12 @@ cpu_init:
         ldr   x0, 
=(TCR_RES1|TCR_SH0_IS|TCR_ORGN0_WBWA|TCR_IRGN0_WBWA|TCR_T0SZ(64-48))
         /* ID_AA64MMFR0_EL1[3:0] (PARange) corresponds to TCR_EL2[18:16] (PS) 
*/
         mrs   x1, ID_AA64MMFR0_EL1
+        /* Limit to 48 bits, 256TB PA range (#5) */
+        ubfm  x1, x1, #0, #3
+        mov   x2, #5
+        cmp   x1, x2
+        csel  x1, x1, x2, lt
+
         bfi   x0, x1, #16, #3
 
         msr   tcr_el2, x0
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index fb71fa4c1c..e5a88095f8 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -2030,7 +2030,7 @@ void __init setup_virt_paging(void)
         unsigned int root_order; /* Page order of the root of the p2m */
         unsigned int sl0;    /* Desired SL0, maximum in comment */
     } pa_range_info[] = {
-        /* T0SZ minimum and SL0 maximum from ARM DDI 0487A.b Table D4-5 */
+        /* T0SZ minimum and SL0 maximum from ARM DDI 0487H.a Table D5-6 */
         /*      PA size, t0sz(min), root-order, sl0(max) */
         [0] = { 32,      32/*32*/,  0,          1 },
         [1] = { 36,      28/*28*/,  0,          1 },
@@ -2038,7 +2038,7 @@ void __init setup_virt_paging(void)
         [3] = { 42,      22/*22*/,  3,          1 },
         [4] = { 44,      20/*20*/,  0,          2 },
         [5] = { 48,      16/*16*/,  0,          2 },
-        [6] = { 0 }, /* Invalid */
+        [6] = { 52,      12/*12*/,  3,          3 },
         [7] = { 0 }  /* Invalid */
     };
 
@@ -2069,10 +2069,13 @@ void __init setup_virt_paging(void)
         }
     }
 
-    /* pa_range is 4 bits, but the defined encodings are only 3 bits */
+    /* pa_range is 4 bits but we don't support all modes */
     if ( pa_range >= ARRAY_SIZE(pa_range_info) || 
!pa_range_info[pa_range].pabits )
         panic("Unknown encoding of ID_AA64MMFR0_EL1.PARange %x\n", pa_range);
 
+    if ( pa_range > 5 )
+        pa_range = 5;
+
     val |= VTCR_PS(pa_range);
     val |= VTCR_TG0_4K;
 
-- 
2.30.2