[Xen-devel] [PATCH v5 2/2] xen/arm: erratum 766422: decode thumb store during data abort

[Julien Grall <julien.grall@xxxxxxxxxx>]

From the errata document:

When a non-secure non-hypervisor memory operation instruction generates a
stage2 page table translation fault, a trap to the hypervisor will be triggered.
For an architecturally defined subset of instructions, the Hypervisor Syndrome
Register (HSR) will have the Instruction Syndrome Valid (ISV) bit set to 1âb1,
and the Rt field should reflect the source register (for stores) or destination
register for loads.
On Cortex-A15, for Thumb and ThumbEE stores, the Rt value may be incorrect
and should not be used, even if the ISV bit is set. All loads, and all ARM
instruction set loads and stores, will have the correct Rt value if the ISV
bit is set.

To avoid this issue, Xen needs to decode thumb store instruction and update
the transfer register.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

---
    Changes in v5:
        - Add gdprintk when the instruction decoding fails
        - s/errata/erratum in patch and commit message
    Changes in v3:
        - Use unlikely to check if the processor is affected by the errata
        - Move the decoder in another patch and use it
    Changes in v2:
        - Only decode the instruction on affected processor
        - Handle ARM 32-bit instruction in read_instruction
---
 xen/arch/arm/traps.c                  |   15 +++++++++++++++
 xen/include/asm-arm/arm32/processor.h |    4 ++++
 xen/include/asm-arm/arm64/processor.h |    2 ++
 3 files changed, 21 insertions(+)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 6b5fa51..a30797c 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -36,6 +36,7 @@
 #include <asm/cpregs.h>
 #include <asm/psci.h>
 
+#include "decode.h"
 #include "io.h"
 #include "vtimer.h"
 #include <asm/gic.h>
@@ -1336,6 +1337,20 @@ static void do_trap_data_abort_guest(struct 
cpu_user_regs *regs,
     if ( !dabt.valid )
         goto bad_data_abort;
 
+    /*
+     * Erratum 766422: Thumb store translation fault to Hypervisor may
+     * not have correct HSR Rt value.
+     */
+    if ( cpu_has_erratum_766422() && (regs->cpsr & PSR_THUMB) && dabt.write )
+    {
+        rc = decode_instruction(regs, &info.dabt);
+        if ( rc )
+        {
+            gdprintk(XENLOG_ERR, "Unable to decode instruction\n");
+            goto bad_data_abort;
+        }
+    }
+
     if (handle_mmio(&info))
     {
         advance_pc(regs, hsr);
diff --git a/xen/include/asm-arm/arm32/processor.h 
b/xen/include/asm-arm/arm32/processor.h
index b266252..d1b89d0 100644
--- a/xen/include/asm-arm/arm32/processor.h
+++ b/xen/include/asm-arm/arm32/processor.h
@@ -111,6 +111,10 @@ struct cpu_user_regs
 #define READ_SYSREG(R...)       READ_SYSREG32(R)
 #define WRITE_SYSREG(V, R...)   WRITE_SYSREG32(V, R)
 
+/* Erratum 766422: only Cortex A15 r0p4 is affected */
+#define cpu_has_erratum_766422()                             \
+    (unlikely(current_cpu_data.midr.bits == 0x410fc0f4))
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __ASM_ARM_ARM32_PROCESSOR_H */
diff --git a/xen/include/asm-arm/arm64/processor.h 
b/xen/include/asm-arm/arm64/processor.h
index c8d4609..5bf0867 100644
--- a/xen/include/asm-arm/arm64/processor.h
+++ b/xen/include/asm-arm/arm64/processor.h
@@ -104,6 +104,8 @@ struct cpu_user_regs
 #define READ_SYSREG(name)     READ_SYSREG64(name)
 #define WRITE_SYSREG(v, name) WRITE_SYSREG64(v, name)
 
+#define cpu_has_erratum_766422() 0
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __ASM_ARM_ARM64_PROCESSOR_H */
-- 
1.7.10.4


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