[PATCH v1] arm64: errata: Workaround NVIDIA Olympus device store/load ordering erratum

[PATCH v1] arm64: errata: Workaround NVIDIA Olympus device store/load ordering erratum

[Shanker Donthineni]

On systems with NVIDIA Olympus cores, a Device-nGnR* load can be
observed by a peripheral before an older, non-overlapping Device-nGnR*
store to the same peripheral. This breaks the program-order guarantee
that software expects for Device-nGnR* accesses and can leave a
peripheral in an incorrect state, as a load is observed before an
earlier store takes effect.

The erratum can occur only when all of the following apply:

  - A PE executes a Device-nGnR* store followed by a younger
    Device-nGnR* load.
  - The store is not a store-release.
  - The accesses target the same peripheral and do not overlap in bytes.
  - There is at most one intervening Device-nGnR* store in program
    order, and there are no intervening Device-nGnR* loads.
  - There is no DSB, and no DMB that orders loads, between the store and
    the load.
  - Specific micro-architectural and timing conditions occur.

Two ways to restore ordering: insert a barrier (any DSB, or a DMB that
orders loads) between the store and the load, or make the store a
store-release. A load-acquire on the load side would not help, because
acquire semantics do not prevent a load from being observed ahead of an
older store; only the store side (release or a barrier) closes the
window.

Promote the raw MMIO store helpers (__raw_writeb/w/l/q) from plain str*
to stlr* (Store-Release), which removes the "store is not a
store-release" condition for every device write the kernel issues.
Because writel() and writel_relaxed() are both built on __raw_writel()
in asm-generic/io.h, patching the raw variants covers both the
non-relaxed and relaxed APIs without touching the higher layers. Note
that writel()'s own barrier sits before the store, so it does not order
the store against a subsequent readl(); the store-release promotion is
what provides that ordering.

Like ARM64_ERRATUM_832075 on the load side, the change is gated on a new
ARM64_WORKAROUND_DEVICE_STORE_RELEASE capability and only activated on
parts that match MIDR_NVIDIA_OLYMPUS, so unaffected CPUs continue to use
the plain str* sequence.

Co-developed-by: Vikram Sethi <vsethi@nvidia.com>
Signed-off-by: Vikram Sethi <vsethi@nvidia.com>
Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 Documentation/arch/arm64/silicon-errata.rst |  2 ++
 arch/arm64/Kconfig                          | 23 ++++++++++++++++++++
 arch/arm64/include/asm/io.h                 | 24 ++++++++++++++-------
 arch/arm64/kernel/cpu_errata.c              |  8 +++++++
 arch/arm64/tools/cpucaps                    |  1 +
 5 files changed, 50 insertions(+), 8 deletions(-)

diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst
index 211119ce7adc..899bed3908bb 100644
--- a/Documentation/arch/arm64/silicon-errata.rst
+++ b/Documentation/arch/arm64/silicon-errata.rst
@@ -256,6 +256,8 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | NVIDIA         | Carmel Core     | N/A             | NVIDIA_CARMEL_CNP_ERRATUM   |
 +----------------+-----------------+-----------------+-----------------------------+
+| NVIDIA         | Olympus core    | T410-OLY-1027   | NVIDIA_OLYMPUS_1027_ERRATUM |
++----------------+-----------------+-----------------+-----------------------------+
 | NVIDIA         | T241 GICv3/4.x  | T241-FABRIC-4   | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
 | NVIDIA         | T241 MPAM       | T241-MPAM-1     | N/A                         |
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fe60738e5943..a6bac84b05a1 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -564,6 +564,29 @@ config ARM64_ERRATUM_832075
 
 	  If unsure, say Y.
 
+config NVIDIA_OLYMPUS_1027_ERRATUM
+	bool "NVIDIA Olympus: device store/load ordering erratum"
+	default y
+	help
+	  This option adds an alternative code sequence to work around an
+	  NVIDIA Olympus core erratum where a Device-nGnR* store can be
+	  observed by a peripheral after a younger Device-nGnR* load to the
+	  same peripheral. This breaks the program order that drivers rely
+	  on for MMIO and can leave a device in an incorrect state.
+
+	  The workaround promotes the raw MMIO store helpers
+	  (__raw_writeb/w/l/q) to Store-Release (STLR), which restores the
+	  required ordering. Because writel() and writel_relaxed() are built
+	  on __raw_writel(), both are covered without changes to the higher
+	  layers.
+
+	  The fix is applied through the alternatives framework, so enabling
+	  this option does not by itself activate the workaround: it is
+	  patched in only when an affected CPU is detected, and is a no-op on
+	  unaffected CPUs.
+
+	  If unsure, say Y.
+
 config ARM64_ERRATUM_834220
 	bool "Cortex-A57: 834220: Stage 2 translation fault might be incorrectly reported in presence of a Stage 1 fault (rare)"
 	depends on KVM
diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index 8cbd1e96fd50..b6d7966e9c19 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -25,29 +25,37 @@
 #define __raw_writeb __raw_writeb
 static __always_inline void __raw_writeb(u8 val, volatile void __iomem *addr)
 {
-	volatile u8 __iomem *ptr = addr;
-	asm volatile("strb %w0, %1" : : "rZ" (val), "Qo" (*ptr));
+	asm volatile(ALTERNATIVE("strb %w0, [%1]",
+				 "stlrb %w0, [%1]",
+				 ARM64_WORKAROUND_DEVICE_STORE_RELEASE)
+		     : : "rZ" (val), "r" (addr));
 }
 
 #define __raw_writew __raw_writew
 static __always_inline void __raw_writew(u16 val, volatile void __iomem *addr)
 {
-	volatile u16 __iomem *ptr = addr;
-	asm volatile("strh %w0, %1" : : "rZ" (val), "Qo" (*ptr));
+	asm volatile(ALTERNATIVE("strh %w0, [%1]",
+				 "stlrh %w0, [%1]",
+				 ARM64_WORKAROUND_DEVICE_STORE_RELEASE)
+		     : : "rZ" (val), "r" (addr));
 }
 
 #define __raw_writel __raw_writel
 static __always_inline void __raw_writel(u32 val, volatile void __iomem *addr)
 {
-	volatile u32 __iomem *ptr = addr;
-	asm volatile("str %w0, %1" : : "rZ" (val), "Qo" (*ptr));
+	asm volatile(ALTERNATIVE("str %w0, [%1]",
+				 "stlr %w0, [%1]",
+				 ARM64_WORKAROUND_DEVICE_STORE_RELEASE)
+		     : : "rZ" (val), "r" (addr));
 }
 
 #define __raw_writeq __raw_writeq
 static __always_inline void __raw_writeq(u64 val, volatile void __iomem *addr)
 {
-	volatile u64 __iomem *ptr = addr;
-	asm volatile("str %x0, %1" : : "rZ" (val), "Qo" (*ptr));
+	asm volatile(ALTERNATIVE("str %x0, [%1]",
+				 "stlr %x0, [%1]",
+				 ARM64_WORKAROUND_DEVICE_STORE_RELEASE)
+		     : : "rZ" (val), "r" (addr));
 }
 
 #define __raw_readb __raw_readb
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 5377e4c2eba2..958d7f16bfeb 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -809,6 +809,14 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		ERRATA_MIDR_ALL_VERSIONS(MIDR_NVIDIA_CARMEL),
 	},
 #endif
+#ifdef CONFIG_NVIDIA_OLYMPUS_1027_ERRATUM
+	{
+		/* NVIDIA Olympus core */
+		.desc = "NVIDIA Olympus device load/store ordering erratum",
+		.capability = ARM64_WORKAROUND_DEVICE_STORE_RELEASE,
+		ERRATA_MIDR_ALL_VERSIONS(MIDR_NVIDIA_OLYMPUS),
+	},
+#endif
 #ifdef CONFIG_ARM64_WORKAROUND_TRBE_OVERWRITE_FILL_MODE
 	{
 		/*
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 811c2479e82d..d367257bf770 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -120,6 +120,7 @@ WORKAROUND_CAVIUM_TX2_219_PRFM
 WORKAROUND_CAVIUM_TX2_219_TVM
 WORKAROUND_CLEAN_CACHE
 WORKAROUND_DEVICE_LOAD_ACQUIRE
+WORKAROUND_DEVICE_STORE_RELEASE
 WORKAROUND_NVIDIA_CARMEL_CNP
 WORKAROUND_PMUV3_IMPDEF_TRAPS
 WORKAROUND_QCOM_FALKOR_E1003
-- 
2.43.0

Re: [PATCH v1] arm64: errata: Workaround NVIDIA Olympus device store/load ordering erratum

[Catalin Marinas]

On Thu, Jun 04, 2026 at 06:12:54PM -0500, Shanker Donthineni wrote:
> On systems with NVIDIA Olympus cores, a Device-nGnR* load can be
> observed by a peripheral before an older, non-overlapping Device-nGnR*
> store to the same peripheral. This breaks the program-order guarantee
> that software expects for Device-nGnR* accesses and can leave a
> peripheral in an incorrect state, as a load is observed before an
> earlier store takes effect.
> 
> The erratum can occur only when all of the following apply:
> 
>   - A PE executes a Device-nGnR* store followed by a younger
>     Device-nGnR* load.
>   - The store is not a store-release.
>   - The accesses target the same peripheral and do not overlap in bytes.
>   - There is at most one intervening Device-nGnR* store in program
>     order, and there are no intervening Device-nGnR* loads.
>   - There is no DSB, and no DMB that orders loads, between the store and
>     the load.
>   - Specific micro-architectural and timing conditions occur.
> 
> Two ways to restore ordering: insert a barrier (any DSB, or a DMB that
> orders loads) between the store and the load, or make the store a
> store-release. A load-acquire on the load side would not help, because
> acquire semantics do not prevent a load from being observed ahead of an
> older store; only the store side (release or a barrier) closes the
> window.

Ignoring Device-nGnR*, a store-release followed by a load (not
load-acquire) would not guarantee any ordering. I assume the
store-release behaviour is specific to this erratum - part of the
preconditions.

The patch looks fine to me.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>