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

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Message-ID: <YxlxAFgW65w8wgPy@nazgul.tnic>
Date:   Thu, 8 Sep 2022 06:35:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>, x86@...nel.org,
        nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
        peterz@...radead.org, 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
Subject: Re: [PATCH -next] memregion: Add arch_flush_memregion() interface

On Wed, Sep 07, 2022 at 09:52:17AM -0700, Dan Williams wrote:
> To be clear nfit stuff and CXL does run in guests, but they do not
> support secure-erase in a guest.
> 
> However, the QEMU CXL enabling is building the ability to do *guest
> physical* address space management, but in that case the driver can be
> paravirtualized to realize that it is not managing host-physical address
> space and does not need to flush caches. That will need some indicator
> to differentiate virtual CXL memory expanders from assigned devices.

Sounds to me like that check should be improved later to ask
whether the kernel is managing host-physical address space, maybe
arch_flush_memregion() should check whether the address it is supposed
to flush is host-physical and exit early if not...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette