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Date: Wed, 6 Jan 2021 11:04:35 +0000 From: Wei Liu <wei.liu@...nel.org> To: Michael Kelley <mikelley@...rosoft.com> Cc: Wei Liu <wei.liu@...nel.org>, Linux on Hyper-V List <linux-hyperv@...r.kernel.org>, "stable@...nel.org" <stable@...nel.org>, KY Srinivasan <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Stephen Hemminger <sthemmin@...rosoft.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] x86/hyperv: check cpu mask after interrupt has been disabled On Tue, Jan 05, 2021 at 06:20:05PM +0000, Michael Kelley wrote: > From: Wei Liu <wei.liu@...nel.org> Sent: Tuesday, January 5, 2021 9:51 AM > > > > We've observed crashes due to an empty cpu mask in > > hyperv_flush_tlb_others. Obviously the cpu mask in question is changed > > between the cpumask_empty call at the beginning of the function and when > > it is actually used later. > > > > One theory is that an interrupt comes in between and a code path ends up > > changing the mask. Move the check after interrupt has been disabled to > > see if it fixes the issue. > > > > Signed-off-by: Wei Liu <wei.liu@...nel.org> > > Cc: stable@...nel.org > > --- > > arch/x86/hyperv/mmu.c | 12 +++++++++--- > > 1 file changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c > > index 5208ba49c89a..2c87350c1fb0 100644 > > --- a/arch/x86/hyperv/mmu.c > > +++ b/arch/x86/hyperv/mmu.c > > @@ -66,11 +66,17 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus, > > if (!hv_hypercall_pg) > > goto do_native; > > > > - if (cpumask_empty(cpus)) > > - return; > > - > > local_irq_save(flags); > > > > + /* > > + * Only check the mask _after_ interrupt has been disabled to avoid the > > + * mask changing under our feet. > > + */ > > + if (cpumask_empty(cpus)) { > > + local_irq_restore(flags); > > + return; > > + } > > + > > flush_pcpu = (struct hv_tlb_flush **) > > this_cpu_ptr(hyperv_pcpu_input_arg); > > > > -- > > 2.20.1 > > Reviewed-by: Michael Kelley <mikelley@...rosoft.com> > Applied to hyperv-fixes. Wei.
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