Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div_u64()

[Oleg Nesterov]

On 07/24, Oleg Nesterov wrote:
> On 07/23, David Laight wrote:
> >
> > On Wed, 23 Jul 2025 11:38:25 +0200
> > Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> > >
> > > to remove the conditional branch and additional variable. Your version
> > > is probably beterr... But this is without WARN/BUG.
> >
> > I wish there was a way of doing a WARN_ONCE from asm with a single instruction.
> > Then you could put one after your 2:
> > Otherwise is it a conditional and a load of inlined code.
> >
> > > So, which version do you prefer?
> >
> > I wish I knew :-)
>
> ;-)
>
> David, you understand this asm magic indefinitely better than me. Plus you are
> working on the generic code. Can you send the patch which looks right to you?
> I agree in advance with anything you do.
>
> I got lost. Now I don't even understand if we want to add BUG and/or WARN into
> mul_u64_u64_div_u64().

Forgot to mention... Not that I think this is a good idea, but if we don't
use BUG/WARN, we can probably add EX_FLAG_ and do something like below.

Oleg.

--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -38,6 +38,9 @@ static bool ex_handler_default(const struct exception_table_entry *e,
 	if (e->data & EX_FLAG_CLEAR_DX)
 		regs->dx = 0;
 
+	if (e->data & EX_FLAG_XXX_AX)
+		regs->ax = -1ul;
+
 	regs->ip = ex_fixup_addr(e);
 	return true;
 }