Re: [PATCH 1/2] x86/setup: consolidate early memory reservations

David Hildenbrand
2021-01-15T10:11:30Z

On 15.01.21 09:32, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> The early reservations of memory areas used by the firmware, bootloader,
> kernel text and data are spread over setup_arch(). Moreover, some of them
> happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
> trim_low_memory_range() are called after reserve_real_mode() that allocates
> memory.
>
> We did not observe corruption of these memory regions because memblock
> always allocates memory either from the end of memory (in top-down mode) or
> above the kernel image (in bottom-up mode). However, the bottom up mode is
> going to be updated to span the entire memory [1] to avoid limitations
> caused by KASLR.
>
> Consolidate early memory reservations in a dedicated function to improve
> robustness against future changes. Having the early reservations in one
> place also makes it clearer what memory must be reserved before we allow
> memblock allocations.
>
> [1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@fb.com
>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> arch/x86/kernel/setup.c | 80 ++++++++++++++++++++++-------------------
> 1 file changed, 44 insertions(+), 36 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 3412c4595efd..32cd2e790a0a 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -728,7 +728,38 @@ static void __init trim_low_memory_range(void)
> */
> memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
> }
> -
> +
> +static void __init early_reserve_memory(void)
> +{
> + /*
> + * Reserve the memory occupied by the kernel between _text and
> + * __end_of_kernel_reserve symbols. Any kernel sections after the
> + * __end_of_kernel_reserve symbol must be explicitly reserved with a
> + * separate memblock_reserve() or they will be discarded.
> + */
> + memblock_reserve(__pa_symbol(_text),
> + (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
> +
> + /*
> + * Make sure page 0 is always reserved because on systems with
> + * L1TF its contents can be leaked to user processes.
> + */
> + memblock_reserve(0, PAGE_SIZE);
> +
> + early_reserve_initrd();
> +
> + if (efi_enabled(EFI_BOOT))
> + efi_memblock_x86_reserve_range();
> +
> + memblock_x86_reserve_range_setup_data();
> +
> + reserve_ibft_region();
> + reserve_bios_regions();
> +
> + trim_platform_memory_ranges();
> + trim_low_memory_range();
> +}
> +
> /*
> * Dump out kernel offset information on panic.
> */
> @@ -763,29 +794,6 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>
> void __init setup_arch(char **cmdline_p)
> {
> - /*
> - * Reserve the memory occupied by the kernel between _text and
> - * __end_of_kernel_reserve symbols. Any kernel sections after the
> - * __end_of_kernel_reserve symbol must be explicitly reserved with a
> - * separate memblock_reserve() or they will be discarded.
> - */
> - memblock_reserve(__pa_symbol(_text),
> - (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
> -
> - /*
> - * Make sure page 0 is always reserved because on systems with
> - * L1TF its contents can be leaked to user processes.
> - */
> - memblock_reserve(0, PAGE_SIZE);
> -
> - early_reserve_initrd();
> -
> - /*
> - * At this point everything still needed from the boot loader
> - * or BIOS or kernel text should be early reserved or marked not
> - * RAM in e820. All other memory is free game.
> - */
> -
> #ifdef CONFIG_X86_32
> memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));
>
> @@ -909,8 +917,18 @@ void __init setup_arch(char **cmdline_p)
>
> parse_early_param();
>
> - if (efi_enabled(EFI_BOOT))
> - efi_memblock_x86_reserve_range();
> + /*
> + * Do some memory reservations *before* memory is added to
> + * memblock, so memblock allocations won't overwrite it.
> + * Do it after early param, so we could get (unlikely) panic from
> + * serial.
> + *
> + * After this point everything still needed from the boot loader or
> + * firmware or kernel text should be early reserved or marked not
> + * RAM in e820. All other memory is free game.
> + */
> + early_reserve_memory();
> +
> #ifdef CONFIG_MEMORY_HOTPLUG
> /*
> * Memory used by the kernel cannot be hot-removed because Linux
> @@ -937,9 +955,6 @@ void __init setup_arch(char **cmdline_p)
>
> x86_report_nx();
>
> - /* after early param, so could get panic from serial */
> - memblock_x86_reserve_range_setup_data();
> -
> if (acpi_mps_check()) {
> #ifdef CONFIG_X86_LOCAL_APIC
> disable_apic = 1;
> @@ -1031,8 +1046,6 @@ void __init setup_arch(char **cmdline_p)
> */
> find_smp_config();
>
> - reserve_ibft_region();
> -
> early_alloc_pgt_buf();
>
> /*
> @@ -1053,8 +1066,6 @@ void __init setup_arch(char **cmdline_p)
> */
> sev_setup_arch();
>
> - reserve_bios_regions();
> -
> efi_fake_memmap();
> efi_find_mirror();
> efi_esrt_init();
> @@ -1080,9 +1091,6 @@ void __init setup_arch(char **cmdline_p)
>
> reserve_real_mode();
>
> - trim_platform_memory_ranges();
> - trim_low_memory_range();
> -
> init_mem_mapping();
>
> idt_setup_early_pf();
>

Did not fully review for side-effects, but looks like a reasonable thing
to do!

--
Thanks,

David / dhildenb