From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 17C431E49F; Mon, 23 Feb 2026 10:55:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771844157; cv=none; b=MxM8m/rG3WEmupOHYMYRa8RQTEZbWXA4h361dXsVKO4NvfMHbZOFwXWMJSkngnYloLDmuRIZCLhyHy6BXFtQHH+6Lswwqb7X2HmQuy4lECAaCtLc0T9dzQjIKmSkAuio3fAVRpmXyjrwz9Wjfv1q3iLJdpX/XArmEmx7MeKZL8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771844157; c=relaxed/simple; bh=Hp/G5bM2cfDXr9AvMTGry72qv+5k5dlSxt17AJXUjBQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=T4QYKx1KH5wKle4yZD8E5dXtPgFueVh01+O6Pc/CKrAttCosRKWeu69zDaltY9+9AHX9A2y9jFKaaJ6R26bfdTS8IazP8PlQiOkK8rnDCrUGYlad7W1lbb6CNtgoyfwJBp3l//ft6m7IJCLqw1vwDT1de3AVuoeK6A1hbsniD20= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PhToeSxe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PhToeSxe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4EAF1C116C6; Mon, 23 Feb 2026 10:55:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771844156; bh=Hp/G5bM2cfDXr9AvMTGry72qv+5k5dlSxt17AJXUjBQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PhToeSxeGI/AfzEciOrUYiCwaquvOzKdmUQQxyn/pTX37XJjk0l/22SEwRHvGkA1b 6uAreg1DXjppT4wPUy+qDmRPKjP8B4WBdgTHA1h05TaDiOCb1/SqAFGapOfBitjYmR /u+Mtmwr2YJkjAAv069cIgmvOoOoDdxoH6CAxdp982qevVQGunRNTkmCBidYz3Nce/ plSnr8T+21sxGn33f3cEo3D2I+LEldHT4G+nbYUIWh3iAuvttW73gnBvbwKwCIllvK FzoDZHO5onuHwH5vGcqU+1EjxesnP78VJ2b5nfK8+6sSaaBCPcDjf550/imijYvFCB I3HhD7AwiozWQ== Date: Mon, 23 Feb 2026 12:55:48 +0200 From: Mike Rapoport To: Ard Biesheuvel Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Benjamin Herrenschmidt , Borislav Petkov , Dave Hansen , Ilias Apalodimas , Ingo Molnar , "H . Peter Anvin" , Thomas Gleixner , linux-efi@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH] x86/efi: defer freeing of boot services memory Message-ID: References: <20260223075219.2348035-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Ard, On Mon, Feb 23, 2026 at 09:08:29AM +0100, Ard Biesheuvel wrote: > Hi Mike, > > On Mon, 23 Feb 2026, at 08:52, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" > > > > efi_free_boot_services() frees memory occupied by EFI_BOOT_SERVICES_CODE > > and EFI_BOOT_SERVICES_DATA using memblock_free_late(). > > > > There are two issue with that: memblock_free_late() should be used for > > memory allocated with memblock_alloc() while the memory reserved with > > memblock_reserve() should be freed with free_reserved_area(). > > > > More acutely, with CONFIG_DEFERRED_STRUCT_PAGE_INIT=y > > efi_free_boot_services() is called before deferred initialization of the > > memory map is complete. > > > > Benjamin Herrenschmidt reports that this causes a leak of ~140MB of > > RAM on EC2 t3a.nano instances which only have 512MB or RAM. > > > > If the freed memory resides in the areas that memory map for them is > > still uninitialized, they won't be actually freed because > > memblock_free_late() calls memblock_free_pages() and the latter skips > > uninitialized pages. > > > > Using free_reserved_area() at this point is also problematic because > > __free_page() accesses the buddy of the freed page and that again might > > end up in uninitialized part of the memory map. > > > > Delaying the entire efi_free_boot_services() could be problematic > > because in addition to freeing boot services memory it updates > > efi.memmap without any synchronization and that's undesirable late in > > boot when there is concurrency. > > > > More robust approach is to only defer freeing of the EFI boot services > > memory. > > > > Make efi_free_boot_services() collect ranges that should be freed into > > an array and add an initcall efi_free_boot_services_memory() that walks > > that array and actually frees the memory using free_reserved_area(). > > > > Instead of creating another table, could we just traverse the EFI memory > map again in the arch_initcall(), and free all boot services code/data > above 1M with EFI_MEMORY_RUNTIME cleared ? Currently efi_free_boot_services() unmaps all boot services code/data with EFI_MEMORY_RUNTIME cleared and removes them from the efi.memmap. I wasn't sure it's Ok to only unmap them, but leave in efi.memmap, that's why I didn't use the existing EFI memory map. Now thinking about it, if the unmapping can happen later, maybe we'll just move the entire efi_free_boot_services() to an initcall? > > Link: > > https://lore.kernel.org/all/ec2aaef14783869b3be6e3c253b2dcbf67dbc12a.camel@kernel.crashing.org > > Fixes: 916f676f8dc0 ("x86, efi: Retain boot service code until after > > switching to virtual mode") > > Cc: > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > arch/x86/include/asm/efi.h | 2 +- > > arch/x86/platform/efi/efi.c | 2 +- > > arch/x86/platform/efi/quirks.c | 55 +++++++++++++++++++++++++++-- > > drivers/firmware/efi/mokvar-table.c | 2 +- > > 4 files changed, 55 insertions(+), 6 deletions(-) > > > > diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h > > index f227a70ac91f..51b4cdbea061 100644 > > --- a/arch/x86/include/asm/efi.h > > +++ b/arch/x86/include/asm/efi.h > > @@ -138,7 +138,7 @@ extern void __init efi_apply_memmap_quirks(void); > > extern int __init efi_reuse_config(u64 tables, int nr_tables); > > extern void efi_delete_dummy_variable(void); > > extern void efi_crash_gracefully_on_page_fault(unsigned long phys_addr); > > -extern void efi_free_boot_services(void); > > +extern void efi_unmap_boot_services(void); > > > > void arch_efi_call_virt_setup(void); > > void arch_efi_call_virt_teardown(void); > > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c > > index d00c6de7f3b7..d84c6020dda1 100644 > > --- a/arch/x86/platform/efi/efi.c > > +++ b/arch/x86/platform/efi/efi.c > > @@ -836,7 +836,7 @@ static void __init __efi_enter_virtual_mode(void) > > } > > > > efi_check_for_embedded_firmwares(); > > - efi_free_boot_services(); > > + efi_unmap_boot_services(); > > > > if (!efi_is_mixed()) > > efi_native_runtime_setup(); > > diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c > > index 553f330198f2..35caa5746115 100644 > > --- a/arch/x86/platform/efi/quirks.c > > +++ b/arch/x86/platform/efi/quirks.c > > @@ -341,7 +341,7 @@ void __init efi_reserve_boot_services(void) > > > > /* > > * Because the following memblock_reserve() is paired > > - * with memblock_free_late() for this region in > > + * with free_reserved_area() for this region in > > * efi_free_boot_services(), we must be extremely > > * careful not to reserve, and subsequently free, > > * critical regions of memory (like the kernel image) or > > @@ -404,17 +404,33 @@ static void __init efi_unmap_pages(efi_memory_desc_t *md) > > pr_err("Failed to unmap VA mapping for 0x%llx\n", va); > > } > > > > -void __init efi_free_boot_services(void) > > +struct efi_freeable_range { > > + u64 start; > > + u64 end; > > +}; > > + > > +static struct efi_freeable_range *ranges_to_free; > > + > > +void __init efi_unmap_boot_services(void) > > { > > struct efi_memory_map_data data = { 0 }; > > efi_memory_desc_t *md; > > int num_entries = 0; > > + int idx = 0; > > + size_t sz; > > void *new, *new_md; > > > > /* Keep all regions for /sys/kernel/debug/efi */ > > if (efi_enabled(EFI_DBG)) > > return; > > > > + sz = sizeof(*ranges_to_free) * efi.memmap.nr_map + 1; > > + ranges_to_free = kzalloc(sz, GFP_KERNEL); > > + if (!ranges_to_free) { > > + pr_err("Failed to allocate storage for freeable EFI regions\n"); > > + return; > > + } > > + > > for_each_efi_memory_desc(md) { > > unsigned long long start = md->phys_addr; > > unsigned long long size = md->num_pages << EFI_PAGE_SHIFT; > > @@ -471,7 +487,15 @@ void __init efi_free_boot_services(void) > > start = SZ_1M; > > } > > > > - memblock_free_late(start, size); > > + /* > > + * With CONFIG_DEFERRED_STRUCT_PAGE_INIT parts of the memory > > + * map are still not initialized and we can't reliably free > > + * memory here. > > + * Queue the ranges to free at a later point. > > + */ > > + ranges_to_free[idx].start = start; > > + ranges_to_free[idx].end = start + size; > > + idx++; > > } > > > > if (!num_entries) > > @@ -512,6 +536,31 @@ void __init efi_free_boot_services(void) > > } > > } > > > > +static int __init efi_free_boot_services(void) > > +{ > > + struct efi_freeable_range *range = ranges_to_free; > > + unsigned long freed = 0; > > + > > + if (!ranges_to_free) > > + return 0; > > + > > + while (range->start) { > > + void *start = phys_to_virt(range->start); > > + void *end = phys_to_virt(range->end); > > + > > + free_reserved_area(start, end, -1, NULL); > > + freed += (end - start); > > + range++; > > + } > > + kfree(ranges_to_free); > > + > > + if (freed) > > + pr_info("Freeing EFI boot services memory: %ldK\n", freed / SZ_1K); > > + > > + return 0; > > +} > > +arch_initcall(efi_free_boot_services); > > + > > /* > > * A number of config table entries get remapped to virtual addresses > > * after entering EFI virtual mode. However, the kexec kernel requires > > diff --git a/drivers/firmware/efi/mokvar-table.c > > b/drivers/firmware/efi/mokvar-table.c > > index 4ff0c2926097..6842aa96d704 100644 > > --- a/drivers/firmware/efi/mokvar-table.c > > +++ b/drivers/firmware/efi/mokvar-table.c > > @@ -85,7 +85,7 @@ static struct kobject *mokvar_kobj; > > * as an alternative to ordinary EFI variables, due to > > platform-dependent > > * limitations. The memory occupied by this table is marked as > > reserved. > > * > > - * This routine must be called before efi_free_boot_services() in order > > + * This routine must be called before efi_unmap_boot_services() in > > order > > * to guarantee that it can mark the table as reserved. > > * > > * Implicit inputs: > > > > base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f > > -- > > 2.51.0 -- Sincerely yours, Mike.