* [PATCH v2] mach-snapdragon: Add early EL2 hypervisor switch support
@ 2026-05-15 6:56 Aswin Murugan
2026-05-15 9:46 ` Sumit Garg
0 siblings, 1 reply; 2+ messages in thread
From: Aswin Murugan @ 2026-05-15 6:56 UTC (permalink / raw)
To: trini, casey.connolly, neil.armstrong, sumit.garg, Michael.Srba,
sjg, aswin.murugan, u-boot-qcom, u-boot
Add support for exiting Gunyah hypervisor and switching to EL2 during
early boot. This is required for platforms that boot U-Boot in a
hypervisor guest environment where U-Boot needs to run at EL2 to
enable other hypervisors like KVM.
The switch is performed via TrustZone SMC call before EL register
configuration in start.S. The implementation:
- Checks current exception level and only executes at EL1
- Uses TrustZone SMC to exit Gunyah and transition to EL2
- Integrates with existing boot0.h infrastructure
A new Kconfig option CONFIG_QCOM_EL2_GUNYAH_EXIT_SUPPORT enables this
functionality.
Signed-off-by: Aswin Murugan <aswin.murugan@oss.qualcomm.com>
---
Change in v2:
- EL2 switch is made at early stage instead of doing at the very last stage in
the previous version
- This change is based on the patch [1]
[1] https://lore.kernel.org/all/20260508-qcom_spl-v7-4-7d0e22aaaa8f@seznam.cz/
Link to v1: https://lore.kernel.org/u-boot/20260419173829.1074404-1-aswin.murugan@oss.qualcomm.com/
---
arch/arm/mach-snapdragon/Kconfig | 7 ++++
arch/arm/mach-snapdragon/include/mach/boot0.h | 3 ++
.../include/mach/gunyah_exit_boot0.h | 36 +++++++++++++++++++
3 files changed, 46 insertions(+)
create mode 100644 arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
diff --git a/arch/arm/mach-snapdragon/Kconfig b/arch/arm/mach-snapdragon/Kconfig
index f863daf6bb9..931d25c1023 100644
--- a/arch/arm/mach-snapdragon/Kconfig
+++ b/arch/arm/mach-snapdragon/Kconfig
@@ -56,6 +56,13 @@ config BOOT0_MSM8916_PSCI_WORKAROUND
help
Select this if you are building U-Boot proper for an msm8916 board that
uses the buggy PSCI implementation.
+
+config QCOM_EL2_GUNYAH_EXIT_SUPPORT
+ bool "Enable early EL2 switch by exiting Gunyah"
+ help
+ Exit Gunyah hypervisor and switch to EL2 during early boot. This must
+ happen before EL register configuration in start.S so that U-Boot can
+ run properly at EL2.
endchoice
endif
diff --git a/arch/arm/mach-snapdragon/include/mach/boot0.h b/arch/arm/mach-snapdragon/include/mach/boot0.h
index b3c76d6d97d..032a9fbdb12 100644
--- a/arch/arm/mach-snapdragon/include/mach/boot0.h
+++ b/arch/arm/mach-snapdragon/include/mach/boot0.h
@@ -1,9 +1,12 @@
/* SPDX-License-Identifier: GPL-2.0+ */
+
#if defined(CONFIG_SPL_BUILD)
b reset
#else
#if defined(CONFIG_BOOT0_MSM8916_PSCI_WORKAROUND)
#include "msm8916_boot0.h"
+#elif defined(CONFIG_QCOM_EL2_GUNYAH_EXIT_SUPPORT)
+#include "gunyah_exit_boot0.h"
#else
b reset
#endif
diff --git a/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h b/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
new file mode 100644
index 00000000000..f69678018ea
--- /dev/null
+++ b/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Early Gunyah Hypervisor Exit
+ *
+ * Exit Gunyah hypervisor and switch to EL2 during early boot. This must
+ * happen before EL register configuration in start.S so that U-Boot can
+ * run properly at EL2.
+ */
+
+#include <linux/arm-smccc.h>
+
+/* TrustZone SMC IDs for hypervisor configuration */
+#define TZ_EL2_SWITCH_SMC_ID 0x02000121
+#define TZ_EL2_SWITCH_PARAM_ID 0x00000023
+#define TZ_EL2_SWITCH_PARAM2_EXIT_GUNYAH 0x1
+
+ /* Save FDT address before we modify x0 */
+ mov x9, x0
+
+ /* Only perform hypervisor switch if we're at EL1 */
+ mrs x0, CurrentEL
+ cmp x0, #(1 << 2)
+ bne 1f
+
+ /* Switch to EL2 (exit Gunyah) */
+ ldr w0, =TZ_EL2_SWITCH_SMC_ID
+ ldr w1, =TZ_EL2_SWITCH_PARAM_ID
+ mov w2, wzr
+ mov w3, wzr
+ ldr w4, =TZ_EL2_SWITCH_PARAM2_EXIT_GUNYAH
+ smc #0
+
+ /* Restore FDT address */
+ mov x0, x9
+1:
+ b reset
--
2.34.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] mach-snapdragon: Add early EL2 hypervisor switch support
2026-05-15 6:56 [PATCH v2] mach-snapdragon: Add early EL2 hypervisor switch support Aswin Murugan
@ 2026-05-15 9:46 ` Sumit Garg
0 siblings, 0 replies; 2+ messages in thread
From: Sumit Garg @ 2026-05-15 9:46 UTC (permalink / raw)
To: Aswin Murugan
Cc: trini, casey.connolly, neil.armstrong, Michael.Srba, sjg,
u-boot-qcom, u-boot
On Fri, May 15, 2026 at 12:26:32PM +0530, Aswin Murugan wrote:
> Add support for exiting Gunyah hypervisor and switching to EL2 during
> early boot. This is required for platforms that boot U-Boot in a
> hypervisor guest environment where U-Boot needs to run at EL2 to
> enable other hypervisors like KVM.
>
> The switch is performed via TrustZone SMC call before EL register
> configuration in start.S. The implementation:
>
> - Checks current exception level and only executes at EL1
> - Uses TrustZone SMC to exit Gunyah and transition to EL2
> - Integrates with existing boot0.h infrastructure
>
> A new Kconfig option CONFIG_QCOM_EL2_GUNYAH_EXIT_SUPPORT enables this
> functionality.
>
> Signed-off-by: Aswin Murugan <aswin.murugan@oss.qualcomm.com>
> ---
> Change in v2:
> - EL2 switch is made at early stage instead of doing at the very last stage in
> the previous version
> - This change is based on the patch [1]
>
> [1] https://lore.kernel.org/all/20260508-qcom_spl-v7-4-7d0e22aaaa8f@seznam.cz/
>
> Link to v1: https://lore.kernel.org/u-boot/20260419173829.1074404-1-aswin.murugan@oss.qualcomm.com/
> ---
> arch/arm/mach-snapdragon/Kconfig | 7 ++++
> arch/arm/mach-snapdragon/include/mach/boot0.h | 3 ++
> .../include/mach/gunyah_exit_boot0.h | 36 +++++++++++++++++++
> 3 files changed, 46 insertions(+)
> create mode 100644 arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
>
> diff --git a/arch/arm/mach-snapdragon/Kconfig b/arch/arm/mach-snapdragon/Kconfig
> index f863daf6bb9..931d25c1023 100644
> --- a/arch/arm/mach-snapdragon/Kconfig
> +++ b/arch/arm/mach-snapdragon/Kconfig
> @@ -56,6 +56,13 @@ config BOOT0_MSM8916_PSCI_WORKAROUND
> help
> Select this if you are building U-Boot proper for an msm8916 board that
> uses the buggy PSCI implementation.
> +
> +config QCOM_EL2_GUNYAH_EXIT_SUPPORT
> + bool "Enable early EL2 switch by exiting Gunyah"
> + help
> + Exit Gunyah hypervisor and switch to EL2 during early boot. This must
> + happen before EL register configuration in start.S so that U-Boot can
> + run properly at EL2.
> endchoice
>
> endif
> diff --git a/arch/arm/mach-snapdragon/include/mach/boot0.h b/arch/arm/mach-snapdragon/include/mach/boot0.h
> index b3c76d6d97d..032a9fbdb12 100644
> --- a/arch/arm/mach-snapdragon/include/mach/boot0.h
> +++ b/arch/arm/mach-snapdragon/include/mach/boot0.h
> @@ -1,9 +1,12 @@
> /* SPDX-License-Identifier: GPL-2.0+ */
> +
> #if defined(CONFIG_SPL_BUILD)
> b reset
> #else
> #if defined(CONFIG_BOOT0_MSM8916_PSCI_WORKAROUND)
> #include "msm8916_boot0.h"
> +#elif defined(CONFIG_QCOM_EL2_GUNYAH_EXIT_SUPPORT)
> +#include "gunyah_exit_boot0.h"
> #else
> b reset
> #endif
> diff --git a/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h b/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
> new file mode 100644
> index 00000000000..f69678018ea
> --- /dev/null
> +++ b/arch/arm/mach-snapdragon/include/mach/gunyah_exit_boot0.h
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Early Gunyah Hypervisor Exit
> + *
> + * Exit Gunyah hypervisor and switch to EL2 during early boot. This must
> + * happen before EL register configuration in start.S so that U-Boot can
> + * run properly at EL2.
> + */
> +
> +#include <linux/arm-smccc.h>
> +
> +/* TrustZone SMC IDs for hypervisor configuration */
> +#define TZ_EL2_SWITCH_SMC_ID 0x02000121
> +#define TZ_EL2_SWITCH_PARAM_ID 0x00000023
> +#define TZ_EL2_SWITCH_PARAM2_EXIT_GUNYAH 0x1
> +
> + /* Save FDT address before we modify x0 */
> + mov x9, x0
> +
> + /* Only perform hypervisor switch if we're at EL1 */
> + mrs x0, CurrentEL
> + cmp x0, #(1 << 2)
> + bne 1f
Above logic is somewhat broken when U-Boot enters in EL2 by default, see
corresponding fix here [1].
Please fold in this fix for v3.
[1] https://github.com/qualcomm-linux/u-boot/pull/64
-Sumit
> +
> + /* Switch to EL2 (exit Gunyah) */
> + ldr w0, =TZ_EL2_SWITCH_SMC_ID
> + ldr w1, =TZ_EL2_SWITCH_PARAM_ID
> + mov w2, wzr
> + mov w3, wzr
> + ldr w4, =TZ_EL2_SWITCH_PARAM2_EXIT_GUNYAH
> + smc #0
> +
> + /* Restore FDT address */
> + mov x0, x9
> +1:
> + b reset
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2026-05-15 6:56 [PATCH v2] mach-snapdragon: Add early EL2 hypervisor switch support Aswin Murugan
2026-05-15 9:46 ` Sumit Garg
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