linux-kernel - Re: [PATCH v9 2/3] x86/boot: Skip video memory access in the decompressor for SEV-ES/SNP

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Date: Mon, 24 Jun 2024 10:03:57 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Ashish Kalra <Ashish.Kalra@....com>, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org
Cc: rafael@...nel.org, hpa@...or.com, peterz@...radead.org,
 adrian.hunter@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 jun.nakajima@...el.com, rick.p.edgecombe@...el.com, michael.roth@....com,
 seanjc@...gle.com, kai.huang@...el.com, bhe@...hat.com,
 kirill.shutemov@...ux.intel.com, bdas@...hat.com, vkuznets@...hat.com,
 dionnaglaze@...gle.com, anisinha@...hat.com, jroedel@...e.de,
 ardb@...nel.org, dyoung@...hat.com, kexec@...ts.infradead.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/3] x86/boot: Skip video memory access in the
 decompressor for SEV-ES/SNP

On 6/20/24 17:23, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> Accessing guest video memory/RAM in the decompressor causes guest
> termination as the boot stage2 #VC handler for SEV-ES/SNP systems does
> not support MMIO handling.
> 
> This issue is observed during a SEV-ES/SNP guest kexec as kexec -c adds
> screen_info to the boot parameters passed to the second kernel, which
> causes console output to be dumped to both video and serial.
> 
> As the decompressor output gets cleared really fast, it is preferable to
> get the console output only on serial, hence, skip accessing the video
> RAM during decompressor stage to prevent guest termination.
> 
> Serial console output during decompressor stage works as boot stage2 #VC
> handler already supports handling port I/O.
> 
>   [ bp: Massage. ]
> 
> Suggested-by: Borislav Petkov (AMD) <bp@...en8.de>
> Suggested-by: Thomas Lendacy <thomas.lendacky@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/boot/compressed/misc.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>