Messages in this thread | | | Date | Thu, 28 May 2020 23:15:50 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}() |
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On Thu, May 28, 2020 at 09:52:30PM +0100, Andrew Cooper wrote: > On 28/05/2020 21:19, Peter Zijlstra wrote: > > --- a/arch/x86/include/asm/debugreg.h > > +++ b/arch/x86/include/asm/debugreg.h > > @@ -113,6 +113,31 @@ static inline void debug_stack_usage_inc > > static inline void debug_stack_usage_dec(void) { } > > #endif /* X86_64 */ > > > > +static __always_inline void local_db_save(unsigned long *dr7) > > +{ > > + get_debugreg(*dr7, 7); > > + if (*dr7) > > + set_debugreg(0, 7); > > %dr7 has an architecturally stuck bit in it. > > You want *dr7 != 0x400 to avoid writing 0 unconditionally.
Do we have to have that bit set when writing it? Otherwise I might actually prefer masking it out.
> Also, API wise, wouldn't it be nicer to write "dr7 = local_db_save()" > rather than having a void function returning a single long via pointer?
Probably.. I started with local_irq_save() and .. well, n/m. I'll change it ;-)
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