arm: Fix asynchronous aborts (SError exceptions) due to bogus PTEs

ARMv8 architecture allows performing prefetch data/instructions
from memory locations marked as normal memory. Prefetch does not
mean that the data/instruction has to be used/executed in code
flow. All PTEs that appear to be valid to MMU must contain valid
physical address with proper attributes otherwise MMU table walk
might cause imprecise asynchronous aborts.

The way current XEN code is preparing page tables for frametable
and xenheap memory can create bogus PTEs. This patch fixes the
issue by clearing page table memory before populating EL2 L0/L1
PTEs. Without this patch XEN crashes on Qualcomm Technologies
server chips due to asynchronous aborts.

The speculative/prefetch feature explanation is scattered everywhere
in ARM specification but below two sections have useful information.

E2.8 Memory types and attributes (ver DDI0487A_h)
G4.12.6 External abort on a translation table walk (ver DDI0487A_h)

Signed-off-by: Vikram Sethi <vikrams@codeaurora.org>
Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Acked-by: Julien Grall <julien.grall@arm.com>

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 0aae6c50fa35d4ab95c6f81094cbf2dccf1754d6..7065c3e6dd93cfd5c15159a14e32eaa6ed44a5ae 100644 (file)
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -730,6 +730,8 @@ void __init setup_xenheap_mappings(unsigned long base_mfn,
         else
         {
             unsigned long first_mfn = alloc_boot_pages(1, 1);
+
+            clear_page(mfn_to_virt(first_mfn));
             pte = mfn_to_xen_entry(first_mfn, WRITEALLOC);
             pte.pt.table = 1;
             write_pte(p, pte);
@@ -773,6 +775,7 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t pe)
     second = mfn_to_virt(second_base);
     for ( i = 0; i < nr_second; i++ )
     {
+        clear_page(mfn_to_virt(second_base + i));
         pte = mfn_to_xen_entry(second_base + i, WRITEALLOC);
         pte.pt.table = 1;
         write_pte(&xen_first[first_table_offset(FRAMETABLE_VIRT_START)+i], pte);