[RFC 14/16] xen/arm: arm64: Add cortex-A57 erratum 832075 workaround

[Julien Grall <julien.grall@arm.com>]

The ARM erratum 832075 applies to certain revisions of Cortex-A57, one
of the workarounds is to change device loads into using load-acquire
semantics.

Use the alternative framework to enable the workaround only on affected
cores.

Whilst a guest could trigger the deadlock, it can be broken when the
processor is receiving an interrupt. As the Xen scheduler will always setup
a timer (firing to every 1ms to 300ms depending on the running time
slice) on each processor, the deadlock would last only few milliseconds
and only affects the guest time slice.

Therefore a malicious guest could only hurt itself. Note that all the
guests should implement/enable the workaround for the affected cores.

Signed-off-by: Julien Grall <julien.grall@arm.com>

---
    Changes in v2:
        - Update the commit message to explain why it is not necessary
        to take care of possible deadlock from the guest.
---
 docs/misc/arm/silicon-errata.txt |  1 +
 xen/arch/arm/Kconfig             | 20 ++++++++++++++++++++
 xen/arch/arm/cpuerrata.c         |  9 +++++++++
 xen/include/asm-arm/arm64/io.h   | 21 +++++++++++++++++----
 xen/include/asm-arm/cpufeature.h |  3 ++-
 xen/include/asm-arm/processor.h  |  2 ++
 6 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/docs/misc/arm/silicon-errata.txt b/docs/misc/arm/silicon-errata.txt
index 9a2983b..ab2e5bc 100644
--- a/docs/misc/arm/silicon-errata.txt
+++ b/docs/misc/arm/silicon-errata.txt
@@ -46,3 +46,4 @@ stable hypervisors.
 | ARM            | Cortex-A53      | #824069         | ARM64_ERRATUM_824069    |
 | ARM            | Cortex-A53      | #819472         | ARM64_ERRATUM_819472    |
 | ARM            | Cortex-A57      | #852523         | N/A                     |
+| ARM            | Cortex-A57      | #832075         | ARM64_ERRATUM_832075    |
diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index 6e4c769..0c3d66d 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -122,6 +122,26 @@ config ARM64_ERRATUM_819472
 	  the kernel if an affected CPU is detected.
 
 	  If unsure, say Y.
+
+config ARM64_ERRATUM_832075
+	bool "Cortex-A57: 832075: possible deadlock on mixing exclusive memory accesses with device loads"
+	default y
+	depends on ARM_64
+	help
+	  This option adds an alternative code sequence to work around ARM
+	  erratum 832075 on Cortex-A57 parts up to r1p2.
+
+	  Affected Cortex-A57 parts might deadlock when exclusive load/store
+	  instructions to Write-Back memory are mixed with Device loads.
+
+	  The workaround is to promote device loads to use Load-Acquire
+	  semantics.
+	  Please note that this does not necessarily enable the workaround,
+	  as it depends on the alternative framework, which will only patch
+	  the kernel if an affected CPU is detected.
+
+	  If unsure, say Y.
+
 endmenu
 
 source "common/Kconfig"
diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
index 211b520..48fc87a 100644
--- a/xen/arch/arm/cpuerrata.c
+++ b/xen/arch/arm/cpuerrata.c
@@ -34,6 +34,15 @@ static const struct arm_cpu_capabilities arm_errata[] = {
         MIDR_RANGE(MIDR_CORTEX_A53, 0x00, 0x01),
     },
 #endif
+#ifdef CONFIG_ARM64_ERRATUM_832075
+    {
+        /* Cortex-A57 r0p0 - r1p2 */
+        .desc = "ARM erratum 832075",
+        .capability = ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE,
+        MIDR_RANGE(MIDR_CORTEX_A57, 0x00,
+                   (1 << MIDR_VARIANT_SHIFT) | 2),
+    },
+#endif
     {},
 };
 
diff --git a/xen/include/asm-arm/arm64/io.h b/xen/include/asm-arm/arm64/io.h
index f80156f..30bfc78 100644
--- a/xen/include/asm-arm/arm64/io.h
+++ b/xen/include/asm-arm/arm64/io.h
@@ -22,6 +22,7 @@
 
 #include <asm/system.h>
 #include <asm/byteorder.h>
+#include <asm/alternative.h>
 
 /*
  * Generic IO read/write.  These perform native-endian accesses.
@@ -49,28 +50,40 @@ static inline void __raw_writeq(u64 val, volatile void __iomem *addr)
 static inline u8 __raw_readb(const volatile void __iomem *addr)
 {
         u8 val;
-        asm volatile("ldrb %w0, [%1]" : "=r" (val) : "r" (addr));
+        asm volatile(ALTERNATIVE("ldrb %w0, [%1]",
+                                 "ldarb %w0, [%1]",
+                                 ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
+                     : "=r" (val) : "r" (addr));
         return val;
 }
 
 static inline u16 __raw_readw(const volatile void __iomem *addr)
 {
         u16 val;
-        asm volatile("ldrh %w0, [%1]" : "=r" (val) : "r" (addr));
+        asm volatile(ALTERNATIVE("ldrh %w0, [%1]",
+                                 "ldarh %w0, [%1]",
+                                 ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
+                     : "=r" (val) : "r" (addr));
         return val;
 }
 
 static inline u32 __raw_readl(const volatile void __iomem *addr)
 {
         u32 val;
-        asm volatile("ldr %w0, [%1]" : "=r" (val) : "r" (addr));
+        asm volatile(ALTERNATIVE("ldr %w0, [%1]",
+                                 "ldar %w0, [%1]",
+                                 ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
+                     : "=r" (val) : "r" (addr));
         return val;
 }
 
 static inline u64 __raw_readq(const volatile void __iomem *addr)
 {
         u64 val;
-        asm volatile("ldr %0, [%1]" : "=r" (val) : "r" (addr));
+        asm volatile(ALTERNATIVE("ldr %0, [%1]",
+                                 "ldar %0, [%1]",
+                                 ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE)
+                     : "=r" (val) : "r" (addr));
         return val;
 }
 
diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index 474a778..78e2263 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -36,8 +36,9 @@
 #define cpu_has_security  (boot_cpu_feature32(security) > 0)
 
 #define ARM64_WORKAROUND_CLEAN_CACHE    0
+#define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE    1
 
-#define ARM_NCAPS           1
+#define ARM_NCAPS           2
 
 #ifndef __ASSEMBLY__
 
diff --git a/xen/include/asm-arm/processor.h b/xen/include/asm-arm/processor.h
index 4123951..a2c0dbe 100644
--- a/xen/include/asm-arm/processor.h
+++ b/xen/include/asm-arm/processor.h
@@ -47,8 +47,10 @@
 #define ARM_CPU_IMP_ARM             0x41
 
 #define ARM_CPU_PART_CORTEX_A53     0xD03
+#define ARM_CPU_PART_CORTEX_A57     0xD07
 
 #define MIDR_CORTEX_A53 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A53)
+#define MIDR_CORTEX_A57 MIDR_CPU_MODEL(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A57)
 
 /* MPIDR Multiprocessor Affinity Register */
 #define _MPIDR_UP           (30)
-- 
1.9.1


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