linux-kernel - Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages

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Date:   Mon, 13 Dec 2021 22:03:48 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, hch@....de,
        robin.murphy@....com, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, vbabka@...e.cz,
        m.szyprowski@...sung.com, John.p.donnelly@...cle.com,
        kexec@...ts.infradead.org, rppt@...ux.ibm.com
Subject: Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when
 no managed pages

On 12/13/21 at 02:25pm, Borislav Petkov wrote:
> 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?

Apparently I didn't. I slacked off and just grabbed things stored in my
brain. This is the right justification and missed. Thanks for pointing
it out.