From: Javier Martinez Canillas javierm@redhat.com
[ Upstream commit a031651ff2144a3d81d4916856c093bc1ea0a413 ]
Commit d9f283ae71af ("efi: Disable runtime services on RT") disabled EFI runtime services by default when the CONFIG_PREEMPT_RT option is enabled.
The rationale for that commit is that some EFI calls could take too much time, leading to large latencies which is an issue for Real-Time kernels.
But a side effect of that change was that now is not possible anymore to enable the EFI runtime services by default when CONFIG_PREEMPT_RT is set, without passing an efi=runtime command line parameter to the kernel.
Instead, let's add a new EFI_DISABLE_RUNTIME boolean Kconfig option, that would be set to n by default but to y if CONFIG_PREEMPT_RT is enabled.
That way, the current behaviour is preserved but gives users a mechanism to enable the EFI runtimes services in their kernels if that is required. For example, if the firmware could guarantee bounded time for EFI calls.
Also, having a separate boolean config could allow users to disable the EFI runtime services by default even when CONFIG_PREEMPT_RT is not set.
Reported-by: Alexander Larsson alexl@redhat.com Fixes: d9f283ae71af ("efi: Disable runtime services on RT") Signed-off-by: Javier Martinez Canillas javierm@redhat.com Link: https://lore.kernel.org/r/20220331151654.184433-1-javierm@redhat.com Signed-off-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/firmware/efi/Kconfig | 15 +++++++++++++++ drivers/firmware/efi/efi.c | 2 +- 2 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig index 2c3dac5ecb36..243882f5e5f9 100644 --- a/drivers/firmware/efi/Kconfig +++ b/drivers/firmware/efi/Kconfig @@ -284,3 +284,18 @@ config EFI_CUSTOM_SSDT_OVERLAYS
See Documentation/admin-guide/acpi/ssdt-overlays.rst for more information. + +config EFI_DISABLE_RUNTIME + bool "Disable EFI runtime services support by default" + default y if PREEMPT_RT + help + Allow to disable the EFI runtime services support by default. This can + already be achieved by using the efi=noruntime option, but it could be + useful to have this default without any kernel command line parameter. + + The EFI runtime services are disabled by default when PREEMPT_RT is + enabled, because measurements have shown that some EFI functions calls + might take too much time to complete, causing large latencies which is + an issue for Real-Time kernels. + + This default can be overridden by using the efi=runtime option. diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index 5502e176d51b..ff57db8f8d05 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -66,7 +66,7 @@ struct mm_struct efi_mm = {
struct workqueue_struct *efi_rts_wq;
-static bool disable_runtime = IS_ENABLED(CONFIG_PREEMPT_RT); +static bool disable_runtime = IS_ENABLED(CONFIG_EFI_DISABLE_RUNTIME); static int __init setup_noefi(char *arg) { disable_runtime = true;