Re: [PATCH v3 1/4] efi/x86: skip efi_arch_mem_reserve() in case of kexec.

[Kuppuswamy Sathyanarayanan]

On 4/4/24 4:11 PM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
>
> For kexec use case, need to use and stick to the EFI memmap passed
> from the first kernel via boot-params/setup data, hence,
> skip efi_arch_mem_reserve() during kexec.
>
> Additionally during SNP guest kexec testing discovered that EFI memmap
> is corrupted during chained kexec. kexec_enter_virtual_mode() during
> late init will remap the efi_memmap physical pages allocated in
> efi_arch_mem_reserve() via memblock & then subsequently cause random
> EFI memmap corruption once memblock is freed/teared-down.
>
> Suggested-by: Dave Young <dyoung@xxxxxxxxxx>
> [Dave Young: checking the md attribute instead of checking the efi_setup]
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> ---
>  arch/x86/platform/efi/quirks.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index f0cc00032751..2b65b3863912 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -255,15 +255,32 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
>  	struct efi_memory_map_data data = { 0 };
>  	struct efi_mem_range mr;
>  	efi_memory_desc_t md;
> -	int num_entries;
> +	int num_entries, ret;
>  	void *new;
>  
> -	if (efi_mem_desc_lookup(addr, &md) ||
> -	    md.type != EFI_BOOT_SERVICES_DATA) {
> +	/*
> +	 * For kexec use case, we need to use the EFI memmap passed from the first
> +	 * kernel via setup data, so we need to skip this.
> +	 * Additionally kexec_enter_virtual_mode() during late init will remap
> +	 * the efi_memmap physical pages allocated here via memboot & then
> +	 * subsequently cause random EFI memmap corruption once memblock is freed.
> +	 */
> +
> +	ret = efi_mem_desc_lookup(addr, &md);

Since you are not using ret, why not directly use if (efi_mem_desc_lookup(..))?

> +	if (ret) {
>  		pr_err("Failed to lookup EFI memory descriptor for %pa\n", &addr);
>  		return;
>  	}
>  
> +	if (md.type != EFI_BOOT_SERVICES_DATA) {
> +		pr_err("Skip reserving non EFI Boot Service Data memory for %pa\n", &addr);
> +		return;
> +	}
> +
> +	/* Kexec copied the efi memmap from the first kernel, thus skip the case */
> +	if (md.attribute & EFI_MEMORY_RUNTIME)
> +		return;
> +
>  	if (addr + size > md.phys_addr + (md.num_pages << EFI_PAGE_SHIFT)) {
>  		pr_err("Region spans EFI memory descriptors, %pa\n", &addr);
>  		return;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer