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Date: Tue, 19 Mar 2024 12:00:15 +0800
From: Dave Young <dyoung@redhat.com>
To: Ashish Kalra <Ashish.Kalra@amd.com>
Cc: tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
	rafael@kernel.org, peterz@infradead.org, adrian.hunter@intel.com,
	sathyanarayanan.kuppuswamy@linux.intel.com,
	elena.reshetova@intel.com, jun.nakajima@intel.com,
	rick.p.edgecombe@intel.com, thomas.lendacky@amd.com,
	seanjc@google.com, michael.roth@amd.com, kai.huang@intel.com,
	bhe@redhat.com, kexec@lists.infradead.org,
	linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
	kirill.shutemov@linux.intel.com, bdas@redhat.com,
	vkuznets@redhat.com, dionnaglaze@google.com, anisinha@redhat.com,
	jroedel@suse.de, Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH v2 1/3] efi/x86: skip efi_arch_mem_reserve() in case of
 kexec.
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References: <20240227212452.3228893-1-kirill.shutemov@linux.intel.com>
 <cover.1710744412.git.ashish.kalra@amd.com>
 <7c2e6ae663da2e5eb41527f0d854f59a56b91ecd.1710744412.git.ashish.kalra@amd.com>
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In-Reply-To: <7c2e6ae663da2e5eb41527f0d854f59a56b91ecd.1710744412.git.ashish.kalra@amd.com>

Hi,

Added Ard in cc.

On 03/18/24 at 07:02am, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> 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 memboot & then subsequently cause random
> EFI memmap corruption once memblock is freed/teared-down.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  arch/x86/platform/efi/quirks.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index f0cc00032751..d4562d074371 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -258,6 +258,16 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
>  	int num_entries;
>  	void *new;
>  
> +	/*
> +	 * 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.

Can you elaborate a bit about the corruption, is it reproducible without
SNP?

> +	 */
> +	if (efi_setup)
> +		return;
> +

How about checking the md attribute instead of checking the efi_setup,
personally I feel it a bit better, something like below:

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index f0cc00032751..699332b075bb 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -255,15 +255,24 @@ 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) {
+	ret = efi_mem_desc_lookup(addr, &md);
+	if (ret) {
 		pr_err("Failed to lookup EFI memory descriptor for %pa\n", &addr);
 		return;
 	}
 
+	if (md.type != EFI_BOOT_SERVICES_DATA) {
+		pr_err("Skil reserving non EFI Boot Service Data memory for %pa\n", &addr);
+		return;
+	}
+
+	/* Kexec copied the efi memmap from the 1st 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;