Re: [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per_sec -4.4% regression

[Michael Ellerman <mpe@ellerman.id.au>]

Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Mon, 5 Aug 2024 at 11:55, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> So please consider this a "maybe something like this" patch, but that
>> 'arch_unmap()' really is pretty nasty
>
> Actually, the whole powerpc vdso code confused me. It's not the vvar
> thing that wants this close thing, it's the other ones that have the
> remap thing.
>
> .. and there were two of those error cases that needed to reset the
> vdso pointer.
>
> That all shows just how carefully I was reading this code.
>
> New version - still untested, but now I've read through it one more
> time - attached.

Needs a slight tweak to compile, vvar_close() needs to return void. And
should probably be renamed vdso_close(). Diff below if anyone else wants
to test it.

I'm testing it now, but it should do what we need.

cheers


diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 6fa041a6690a..431b46976db8 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -81,8 +81,8 @@ static int vdso64_mremap(const struct vm_special_mapping *sm, struct vm_area_str
 	return vdso_mremap(sm, new_vma, &vdso64_end - &vdso64_start);
 }
 
-static int vvar_close(const struct vm_special_mapping *sm,
-		      struct vm_area_struct *vma)
+static void vdso_close(const struct vm_special_mapping *sm,
+                       struct vm_area_struct *vma)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	mm->context.vdso = NULL;
@@ -99,13 +99,13 @@ static struct vm_special_mapping vvar_spec __ro_after_init = {
 static struct vm_special_mapping vdso32_spec __ro_after_init = {
 	.name = "[vdso]",
 	.mremap = vdso32_mremap,
-	.close = vvar_close,
+	.close = vdso_close,
 };
 
 static struct vm_special_mapping vdso64_spec __ro_after_init = {
 	.name = "[vdso]",
 	.mremap = vdso64_mremap,
-	.close = vvar_close,
+	.close = vdso_close,
 };
 
 #ifdef CONFIG_TIME_NS