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Date:   Fri, 21 Jun 2019 17:33:28 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jacob Pan <jacob.jun.pan@intel.com>
cc:     Stephane Eranian <eranian@google.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
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        Ricardo Neri <ricardo.neri@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Wincy Van <fanwenyi0529@gmail.com>,
        Ashok Raj <ashok.raj@intel.com>, x86 <x86@kernel.org>,
        Andi Kleen <andi.kleen@intel.com>,
        Borislav Petkov <bp@suse.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Juergen Gross <jgross@suse.com>,
        Tony Luck <tony.luck@intel.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        iommu@lists.linux-foundation.org,
        Philippe Ombredanne <pombredanne@nexb.com>
Subject: Re: [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt
 remampping table entry for watchdog
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On Wed, 19 Jun 2019, Jacob Pan wrote:
> On Tue, 18 Jun 2019 01:08:06 +0200 (CEST)
> Thomas Gleixner <tglx@linutronix.de> wrote:
> > 
> > Unless this problem is not solved and I doubt it can be solved after
> > talking to IOMMU people and studying manuals,
>
> I agree. modify irte might be done with cmpxchg_double() but the queued
> invalidation interface for IRTE cache flush is shared with DMA and
> requires holding a spinlock for enque descriptors, QI tail update etc.
> 
> Also, reserving & manipulating IRTE slot for hpet via backdoor might not
> be needed if the HPET PCI BDF (found in ACPI) can be utilized. But it
> might need more work to add a fake PCI device for HPET.

What would PCI/BDF solve?

Thanks,

	tglx