Re: kexec regression since 4.9 caused by efi

Ard Biesheuvel
2017-03-17T13:25:33Z

On 17 March 2017 at 02:09, Dave Young <dyoung-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> On 03/16/17 at 12:41pm, Matt Fleming wrote:
>> On Mon, 13 Mar, at 03:37:48PM, Dave Young wrote:
>> >
>> > Omar, could you try below patch? Looking at the efi_mem_desc_lookup, it is not
>> > correct to be used in efi_arch_mem_reserve, if it passed your test, I
>> > can rewrite patch log with more background and send it out:
>> >
>> > for_each_efi_memory_desc(md) {
>> > [snip]
>> > if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
>> > md->type != EFI_BOOT_SERVICES_DATA &&
>> > md->type != EFI_RUNTIME_SERVICES_DATA) {
>> > continue;
>> > }
>> >
>> > In above code, it meant to get a md of EFI_MEMORY_RUNTIME of either boot
>> > data or runtime data, this is wrong for efi_mem_reserve, because we are
>> > reserving boot data which has no EFI_MEMORY_RUNTIME attribute at the
>> > running time. Just is happened to work and we did not capture the error.
>>
>> Wouldn't something like this be simpler?
>>
>> ---
>>
>> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
>> index 30031d5293c4..cdfe8c628959 100644
>> --- a/arch/x86/platform/efi/quirks.c
>> +++ b/arch/x86/platform/efi/quirks.c
>> @@ -201,6 +201,10 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
>> return;
>> }
>>
>> + /* No need to reserve regions that will never be freed. */
>> + if (md.attribute & EFI_MEMORY_RUNTIME)
>> + return;
>> +
>
> Matt, I think it should be fine although I think the md type checking in
> efi_mem_desc_lookup() is causing confusion and not easy to understand..
>
> How about move the if chunk early like below because it seems no need
> to sanity check the addr + size any more if the md is still RUNTIME?
>
> --- linux-x86.orig/arch/x86/platform/efi/quirks.c
> +++ linux-x86/arch/x86/platform/efi/quirks.c
> @@ -196,6 +196,10 @@ void __init efi_arch_mem_reserve(phys_ad
> return;
> }
>
> + /* No need to reserve regions that will never be freed. */
> + 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;
>

This way, we suppress the error it the region spans multiple
descriptors, and only the first one has the runtime attribute. So the
two patches are not equivalent. I don't have a strong preference
either way, though.