Messages in this thread Patch in this message | | | Date | Mon, 27 Apr 2015 10:46:31 +0200 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader |
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On Mon, Apr 27, 2015 at 03:16:00AM +0000, Zheng, Lv wrote: > > @@ -840,7 +840,9 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs) > > struct ghes *ghes; > > int sev, ret = NMI_DONE; > > > > - raw_spin_lock(&ghes_nmi_lock); > > + if (!atomic_add_unless(&ghes_in_nmi, 1, 1)) > > + return ret; > > + > > Just a simple question. > Why not just using cmpxchg here instead of atomic_add_unless so that no atomic_dec will be needed.
What do you think atomic_add_unless ends up doing:
#APP # 177 "./arch/x86/include/asm/atomic.h" 1 .pushsection .smp_locks,"a" .balign 4 .long 671f - . .popsection 671: lock; cmpxchgl %edx,ghes_in_nmi(%rip) # D.37056, MEM[(volatile u32 *)&ghes_in_nmi] # 0 "" 2 #NO_APP
And you need to atomic_dec() so that another reader can enter, i.e. how the exclusion primitive works.
Or did you have something else in mind?
-- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --
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