linux-kernel - RE: [PATCH -next] memregion: Add arch_flush

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Date:   Mon, 29 Aug 2022 16:02:22 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Davidlohr Bueso <dave@...olabs.net>, <dan.j.williams@...el.com>
CC:     <x86@...nel.org>, <nvdimm@...ts.linux.dev>,
        <linux-cxl@...r.kernel.org>, <peterz@...radead.org>,
        <bp@...en8.de>, <akpm@...ux-foundation.org>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
        <a.manzanares@...sung.com>, <linux-kernel@...r.kernel.org>,
        <dave@...olabs.net>, <hch@....de>
Subject: RE: [PATCH -next] memregion: Add arch_flush_memregion() interface

[ add Christoph ]

Davidlohr Bueso wrote:
> With CXL security features, global CPU cache flushing nvdimm requirements
> are no longer specific to that subsystem, even beyond the scope of
> security_ops. CXL will need such semantics for features not necessarily
> limited to persistent memory.
> 
> The functionality this is enabling is to be able to instantaneously
> secure erase potentially terabytes of memory at once and the kernel
> needs to be sure that none of the data from before the secure is still
> present in the cache. It is also used when unlocking a memory device
> where speculative reads and firmware accesses could have cached poison
> from before the device was unlocked.
> 
> This capability is typically only used once per-boot (for unlock), or
> once per bare metal provisioning event (secure erase), like when handing
> off the system to another tenant or decommissioning a device.
> 
> Users must first call arch_has_flush_memregion() to know whether this
> functionality is available on the architecture. Only enable it on x86-64
> via the wbinvd() hammer.
> 
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> ---
> 
> Changes from v2 (https://lore.kernel.org/all/20220819171024.1766857-1-dave@stgolabs.net/):
> - Redid to use memregion based interfaces + VMM check on x86 (Dan)
> - Restricted the flushing to x86-64.
> 
> Note: Since we still are dealing with a physical "range" at this level,
> added the spa range for nfit even though this is unused.

Looks reasonable to me.

Reviewed-by: Dan Williams <dan.j.williams@...el.com>