Hi Baoquan,
On Tue, Jun 01, 2021 at 05:06:53PM +0800, Baoquan He wrote:
> On 06/01/21 at 10:53am, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> ......
>
> > diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> > index 7850111008a8..b15ebfe40a73 100644
> > --- a/arch/x86/platform/efi/quirks.c
> > +++ b/arch/x86/platform/efi/quirks.c
> > @@ -450,6 +450,18 @@ void __init efi_free_boot_services(void)
> > size -= rm_size;
> > }
>
> Thanks for taking care of the low-1M excluding in
> efi_free_boot_services(), Mike. You might want to remove the old real
> mode excluding code either since it's been covered by your new code.
Unfortunately I can't because it's important that set_real_mode_mem() would
reuse memory that was occupied by EFI boot services and that is being freed
here.
According to the changelog of 5bc653b73182 ("x86/efi: Allocate a trampoline
if needed in efi_free_boot_services()"), that system has EBDA at 0x2c000 so
we reserve everything from 0x2c000 to 0xa0000 in reserve_bios_regions() and
most of the memory below 0x2c0000 is used by EFI boot data. So with such
memory layout reserve_real_mode() won't be able to allocate the trampoline.
Yet, when the EFI boot data is free, the room occupied by it will be reused
by the real mode trampoline via set_real_mode_mem().
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index b15ebfe40a73..be814f2089ff 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -409,7 +409,6 @@ void __init efi_free_boot_services(void)
> for_each_efi_memory_desc(md) {
> unsigned long long start = md->phys_addr;
> unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
> - size_t rm_size;
>
> if (md->type != EFI_BOOT_SERVICES_CODE &&
> md->type != EFI_BOOT_SERVICES_DATA) {
> @@ -430,26 +429,6 @@ void __init efi_free_boot_services(void)
> */
> efi_unmap_pages(md);
>
> - /*
> - * Nasty quirk: if all sub-1MB memory is used for boot
> - * services, we can get here without having allocated the
> - * real mode trampoline. It's too late to hand boot services
> - * memory back to the memblock allocator, so instead
> - * try to manually allocate the trampoline if needed.
> - *
> - * I've seen this on a Dell XPS 13 9350 with firmware
> - * 1.4.4 with SGX enabled booting Linux via Fedora 24's
> - * grub2-efi on a hard disk. (And no, I don't know why
> - * this happened, but Linux should still try to boot rather
> - * panicking early.)
> - */
> - rm_size = real_mode_size_needed();
> - if (rm_size && (start + rm_size) < (1<<20) && size >= rm_size) {
> - set_real_mode_mem(start);
> - start += rm_size;
> - size -= rm_size;
> - }
> -
> /*
> * Don't free memory under 1M for two reasons:
> * - BIOS might clobber it
>
> >
> > + /*
> > + * Don't free memory under 1M for two reasons:
> > + * - BIOS might clobber it
> > + * - Crash kernel needs it to be reserved
> > + */
> > + if (start + size < SZ_1M)
> > + continue;
> > + if (start < SZ_1M) {
> > + size -= (SZ_1M - start);
> > + start = SZ_1M;
> > + }
> > +
> > memblock_free_late(start, size);
> > }
> >
> > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> > index 2e1c1bec0f9e..8ea285aca827 100644
> > --- a/arch/x86/realmode/init.c
> > +++ b/arch/x86/realmode/init.c
> > @@ -29,14 +29,16 @@ void __init reserve_real_mode(void)
> >
> > /* Has to be under 1M so we can execute real-mode AP code. */
> > mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
> > - if (!mem) {
> > + if (!mem)
> > pr_info("No sub-1M memory is available for the trampoline\n");
> > - return;
> > - }
> > + else
> > + set_real_mode_mem(mem);
> >
> > - memblock_reserve(mem, size);
> > - set_real_mode_mem(mem);
> > - crash_reserve_low_1M();
> > + /*
> > + * Unconditionally reserve the entire fisrt 1M, see comment in
> > + * setup_arch()
> > + */
> > + memblock_reserve(0, SZ_1M);
> > }
> >
> > static void sme_sev_setup_real_mode(struct trampoline_header *th)
> > --
> > 2.28.0
> >
>
--
Sincerely yours,
Mike.
