Le 05/11/2022 à 09:00, Christophe Leroy a écrit :

Le 04/11/2022 à 18:27, Andrew Donnellan a écrit :

quoted

powerpc unfortunately has too many places where we run stuff in real mode.

With CONFIG_VMAP_STACK enabled, this means we need to be able to swap the
stack pointer to use the linear mapping when we enter a real mode section,
and back afterwards.

Store the top bits of the stack pointer in both the linear map and the
vmalloc space in the PACA, and add some helper macros/functions to swap
between them.

That may work when pagesize is 64k because stack is on a single page,
but I doubt is works with 4k pages, because vmalloc may allocate non
contiguous pages.

[snip]

quoted

+
+#else // __ASSEMBLY__
+
+#include <asm/paca.h>
+#include <asm/reg.h>
+#include <linux/mm.h>
+
+#define stack_pa(ptr) (is_vmalloc_addr((ptr)) ? (void *)vmalloc_to_phys((void *)(ptr)) : (void *)ptr)
+
+static __always_inline void swap_stack_linear(void)
+{
+	current_stack_pointer = get_paca()->kstack_linear_base |	\
+		(current_stack_pointer & (THREAD_SIZE - 1));

That looks hacky. I think you can't just change current_stack_pointer on
the fly. You have to provide something similar to call_do_softirq() or
call_do_irq()

Maybe you can have a look at Nic's RFC for calling functions in real 
mode : 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210212012041.392566-1-npiggin@gmail.com/

Christophe