Re: [PATCH v3 3/4] x86/boot/compressed: Skip Video Memory access in Decompressor for SEV-ES/SNP.

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 4/4/24 4:11 PM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> Accessing guest video memory/RAM during kernel decompressor
> causes guest termination as boot stage2 #VC handler for
> SEV-ES/SNP systems does not support MMIO handling.
>
> This issue is observed with SEV-ES/SNP guest kexec as
> kexec -c adds screen_info to the boot parameters
> passed to the kexec 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 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.
>
> Suggested-by: Thomas Lendacy <thomas.lendacky@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  arch/x86/boot/compressed/misc.c | 6 ++++--
>  arch/x86/boot/compressed/misc.h | 1 +
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index b70e4a21c15f..47b4db200e1f 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -427,8 +427,10 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
>  		vidport = 0x3d4;
>  	}
>  
> -	lines = boot_params_ptr->screen_info.orig_video_lines;
> -	cols = boot_params_ptr->screen_info.orig_video_cols;
> +	if (!sev_es_enabled()) {
> +		lines = boot_params_ptr->screen_info.orig_video_lines;
> +		cols = boot_params_ptr->screen_info.orig_video_cols;
> +	}
>  
>  	init_default_io_ops();
>  
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index b353a7be380c..3c12ca987554 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -37,6 +37,7 @@
>  #include <asm/desc_defs.h>
>  
>  #include "tdx.h"
> +#include "sev.h"
>  
>  #define BOOT_CTYPE_H
>  #include <linux/acpi.h>

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer