Re: [RFC PATCH 0/1] DOE usage with pcie/portdrv

From: Dan Williams <dan.j.williams@intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Christoph Hellwig <hch@infradead.org>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Gavin Hindman <gavin.hindman@intel.com>,
	Linuxarm <linuxarm@huawei.com>,
	"Weiny, Ira" <ira.weiny@intel.com>,
	Linux PCI <linux-pci@vger.kernel.org>,
	linux-cxl@vger.kernel.org, CHUCK_LEVER <chuck.lever@oracle.com>
Subject: Re: [RFC PATCH 0/1] DOE usage with pcie/portdrv
Date: Fri, 20 May 2022 08:37:50 -0700	[thread overview]
Message-ID: <CAPcyv4iWGb7baQSsjjLJFuT1E11X8cHYdZoGXsNd+B9GHtsxLw@mail.gmail.com> (raw)
In-Reply-To: <20220520054214.GB22631@wunner.de>

On Thu, May 19, 2022 at 10:42 PM Lukas Wunner <lukas@wunner.de> wrote:
>
> On Wed, May 18, 2022 at 06:43:39AM -0700, Christoph Hellwig wrote:
> > On Sat, May 14, 2022 at 03:55:21PM +0200, Lukas Wunner wrote:
> > > Circling back to the SPDM/IDE topic, while NVMe is now capable of
> > > reliably recovering from errors, it does expect the kernel to handle
> > > recovery within a few seconds.  I'm not sure we can continue to
> > > guarantee that if the kernel depends on user space to perform
> > > re-authentication with SPDM after reset.  That's another headache
> > > that we could avoid with in-kernel SPDM authentication.
> >
> > I wonder if we need kernel bundled and tightly controlled userspace
> > code for these kinds of things (also for NVMe/NFS TLS).  That is,
> > bundle a userspace ELF file or files with a module which is unpacked
> > to or accessible by a ramfs-style file systems.  Then allow executing
> > it without any interaction with the normal userspace, and non-pagable
> > memory.  That way we can reuse existing userspace code, have really
> > nice address space isolation but avoid all the deadlock potential
> > of normal userspace code.  And I don't think it would be too hard to
> > implement either.
>
> Just as a reminder, on resume from system sleep, IDE needs to be
> set up by pci_pm_resume_noirq() to comply with the existing assumption
> that a PCI driver's ->resume_noirq callback may access the device.
>
> At that point (device) interrupts are disabled, so it's not possible
> to e.g. read certificates from disk or perform an OCSP request.
> So the bundled userspace code would have to conform to a number of
> severe restrictions to avoid resume issues.

Recall that OS managed IDE is somewhat of a stop-gap / special case as
typically the OS kernel is outside of the platform trust boundary for
things like TDX. I imagine suspend in the presence of IDE would be
platform firmware managed, not OS managed. Certificate validation can
always move internal to the kernel later if a concrete need arises,
but it is difficult to go the other way, to kick out certificate
validation from the kernel if it proves not to be needed. Otherwise, a
ring3/ userspace helper that can live in non-pageable memory to avoid
scenarios like this sounds like a capability that would be worth
having regardless.