Date:   Mon, 13 Dec 2021 14:25:39 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
        linux-mm@kvack.org, akpm@linux-foundation.org, hch@lst.de,
        robin.murphy@arm.com, cl@linux.com, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz,
        m.szyprowski@samsung.com, John.p.donnelly@oracle.com,
        kexec@lists.infradead.org, rppt@linux.ibm.com
Subject: Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when
 no managed pages
Message-ID: <YbdJ00wRFvi0aqze@zn.tnic>
References: <20211207030750.30824-1-bhe@redhat.com>
 <20211207031631.GA5604@MiWiFi-R3L-srv>
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On Tue, Dec 07, 2021 at 11:16:31AM +0800, Baoquan He wrote:
> > This low 1M lock down is needed because AMD SME encrypts memory making
> > the old backup region mechanims impossible when switching into kdump
> > kernel. And Intel engineer mentioned their TDX (Trusted domain extensions)
> > which is under development in kernel also needs lock down the low 1M.
> > So we can't simply revert above commits to fix the page allocation
> > failure from DMA zone as someone suggested.

Did you read

  f1d4d47c5851 ("x86/setup: Always reserve the first 1M of RAM")

carefully for a more generically important reason as to why the first 1M
should not be used?

-- 
Regards/Gruss,
    Boris.

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