[PATCH v10] um: Enable preemption in UML

[Anton Ivanov]

On 02/07/2024 09:25, Johannes Berg wrote:
> From: Anton Ivanov <anton.ivanov at cambridgegreys.com>
> 
> Since userspace state is saved in the MM process, kernel using
> FPU still doesn't really need to do anything, so this really
> is as simple as enabling preemption. The irq critical section
> in sigio_handler() needs preempt_disable()/preempt_enable().
> 
> Signed-off-by: Anton Ivanov <anton.ivanov at cambridgegreys.com>
> [vastly simplify, fix x86/um Makefile, rewrite commit message]
> Signed-off-by: Johannes Berg <johannes.berg at intel.com>
> ---
> v10:
>   - rebase on top of various other patchsets, including Benjamin's
>     page table updates: https://patchwork.ozlabs.org/project/linux-um/list/?series=408104
>   - fix x86/um Makefile
>   - remove FPU save/restore code since it's not needed
> ---
>   arch/um/Kconfig      | 2 +-
>   arch/um/kernel/irq.c | 2 ++
>   arch/x86/um/Makefile | 1 -
>   3 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> index 1faefc0a18ea..dca84fd6d00a 100644
> --- a/arch/um/Kconfig
> +++ b/arch/um/Kconfig
> @@ -11,7 +11,7 @@ config UML
>   	select ARCH_HAS_KCOV
>   	select ARCH_HAS_STRNCPY_FROM_USER
>   	select ARCH_HAS_STRNLEN_USER
> -	select ARCH_NO_PREEMPT
> +	select ARCH_NO_PREEMPT_DYNAMIC
>   	select HAVE_ARCH_AUDITSYSCALL
>   	select HAVE_ARCH_KASAN if X86_64
>   	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
> diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
> index ceda4bd2e5ed..534e91797f89 100644
> --- a/arch/um/kernel/irq.c
> +++ b/arch/um/kernel/irq.c
> @@ -238,7 +238,9 @@ static void _sigio_handler(struct uml_pt_regs *regs,
>   
>   void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
>   {
> +	preempt_disable();
>   	_sigio_handler(regs, irqs_suspended);
> +	preempt_enable();
>   }
>   
>   static struct irq_entry *get_irq_entry_by_fd(int fd)
> diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile
> index 17b85209c43d..36e67fc97c22 100644
> --- a/arch/x86/um/Makefile
> +++ b/arch/x86/um/Makefile
> @@ -31,7 +31,6 @@ obj-y += syscalls_64.o vdso/
>   
>   subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o \
>   	../lib/memmove_64.o ../lib/memset_64.o
> -subarch-$(CONFIG_PREEMPTION) += ../entry/thunk_64.o
>   
>   endif
>   

Is that all we have left? I lost track of your mm patches and they do not apply cleanly to master at present.

Otherwise, the fpu-less on top of the older mm works fine for me. Testing it at the moment.

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/