Re: [PATCH v3.1 2/4] efi/arm: preserve early mapping of UEFI memory map longer for BGRT

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>,
	AKASHI Takahiro <takahiro.akashi@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	"Baicar, Tyler" <tbaicar@codeaurora.org>,
	Bhupesh Sharma <bhsharma@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Al Stone <al.stone@linaro.org>,
	Graeme Gregory <graeme.gregory@linaro.org>,
	Hanjun Guo <hanjun.guo@linaro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Kexec Mailing List <kexec@lists.infradead.org>
Subject: Re: [PATCH v3.1 2/4] efi/arm: preserve early mapping of UEFI memory map longer for BGRT
Date: Thu, 12 Jul 2018 16:14:00 +0200	[thread overview]
Message-ID: <CAKv+Gu_+XcOFfJBhVaQp3yUZ36Q5gS47vJzFMniwQ2DZp062tw@mail.gmail.com> (raw)
In-Reply-To: <20180712133220.GA21647@arm.com>

On 12 July 2018 at 15:32, Will Deacon <will.deacon@arm.com> wrote:
> On Tue, Jul 10, 2018 at 08:39:16PM +0200, Ard Biesheuvel wrote:
>> On 10 July 2018 at 19:57, James Morse <james.morse@arm.com> wrote:
>> > Hi Ard,
>> >
>> > On 10/07/18 00:42, AKASHI Takahiro wrote:
>> >> From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> >>
>> >> The BGRT code validates the contents of the table against the UEFI
>> >> memory map, and so it expects it to be mapped when the code runs.
>> >>
>> >> On ARM, this is currently not the case, since we tear down the early
>> >> mapping after efi_init() completes, and only create the permanent
>> >> mapping in arm_enable_runtime_services(), which executes as an early
>> >> initcall, but still leaves a window where the UEFI memory map is not
>> >> mapped.
>> >>
>> >> So move the call to efi_memmap_unmap() from efi_init() to
>> >> arm_enable_runtime_services().
>> >
>> > I don't have a machine that generates a BGRT, but I can see that efi_mem_type()
>> > call in efi_bgrt_init() would cause the same problems we have with kexec and acpi.
>> >
>>
>> I'm not sure I follow. The BGRT table only contains natively aligned
>> fields, so the alignment faults should not occur when accessing this
>> table after kexec. The issue addressed by this patch is that
>> efi_mem_type() bails when called while EFI_MEMMAP is cleared.
>>
>> >
>> >> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
>> >> index b5214c143fee..388a929baf95 100644
>> >> --- a/drivers/firmware/efi/arm-init.c
>> >> +++ b/drivers/firmware/efi/arm-init.c
>> >> @@ -259,7 +259,6 @@ void __init efi_init(void)
>> >>
>> >>       reserve_regions();
>> >>       efi_esrt_init();
>> >> -     efi_memmap_unmap();
>> >>
>> >>       memblock_reserve(params.mmap & PAGE_MASK,
>> >>                        PAGE_ALIGN(params.mmap_size +
>> >> diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
>> >> index 5889cbea60b8..59a8c0ec94d5 100644
>> >> --- a/drivers/firmware/efi/arm-runtime.c
>> >> +++ b/drivers/firmware/efi/arm-runtime.c
>> >> @@ -115,6 +115,8 @@ static int __init arm_enable_runtime_services(void)
>> >>               return 0;
>> >>       }
>> >>
>> >> +     efi_memmap_unmap();
>> >
>> > This can get called twice if uefi_init() fails after setting the EFI_BOOT flag,
>> > but this can only happen if the system table signature is wrong, (or we're out
>> > of memory really early).
>> >
>>
>> I guess we should check the EFI_MEMMAP attribute here as well then.
>
> Do you plan to spin a new version of this patch?
>

Either that or fold in the hunk below.

--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c
@@ -110,7 +110,7 @@ static int __init arm_enable_runtime_services(void)
 {
        u64 mapsize;

-       if (!efi_enabled(EFI_BOOT)) {
+       if (!efi_enabled(EFI_BOOT) || !efi_enabled(EFI_MEMMAP)) {
                pr_info("EFI services will not be available.\n");
                return 0;
        }
