linux-kernel - Re: [PATCH] nvme: Enable acceleration feature of A64FX processor

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Message-ID: <20190222170715.GA10237@localhost.localdomain>
Date:   Fri, 22 Feb 2019 10:07:15 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Takao Indoh <indou.takao@...itsu.com>
Cc:     "Elliott, Robert (Persistent Memory)" <elliott@....com>,
        Takao Indoh <indou.takao@...fujitsu.com>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "axboe@...com" <axboe@...com>, "hch@....de" <hch@....de>
Subject: Re: [PATCH] nvme: Enable acceleration feature of A64FX processor

On Wed, Feb 20, 2019 at 06:46:11PM +0900, Takao Indoh wrote:
> On Thu, Feb 14, 2019 at 08:44:48PM +0000, Elliott, Robert (Persistent Memory) wrote:
> > * how does this interact with an iommu, if there is one? Must the 
> > address with bit 56 also be granted permission, or is that
> > stripped off before any iommu comparisons?
> 
> The latter. A bit 56 is cleared in Root Port before pass it to iommu.

What if the intendend destination is a peer and never hits the root port?

Really, though, PCI device vendors need to just use the existing
capability as intended and not have arch specific work-arounds. I'm sure
nvme can't be the only device class you'd want this behavior.