Re: [RFC][PATCH 06/34] x86/boot: Use consistent value for iomem_resource.end

Huang, Kai
2024-02-27T10:59:58Z

On Thu, 2024-02-22 at 10:39 -0800, Dave Hansen wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> The 'struct cpuinfo_x86' values (including 'boot_cpu_info') get
> written and overwritten rather randomly. They are not stable
> during early boot and readers end up getting a random mishmash
> of hard-coded defaults or CPUID-provided values based on when
> the values are read.
>
> iomem_resource.end is one of these users. Because of where it
> is called, it ended up seeing .x86_phys_bits==MAX_PHYSMEM_BITS
> which is (mostly) a compile-time default. But
> iomem_resource.end is never updated if the runtime CPUID
> x86_phys_bits is lower.
>
> Set iomem_resource.end to the compile-time value explicitly.
> It does not need to be precise as this is mostly to ensure
> that insane values can't be reserved in 'iomem_resource'.
>
> Make MAX_PHYSMEM_BITS available outside of sparsemem
> configurations by removing the #ifdef CONFIG_SPARSEMEM in the
> header.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> ---
>
> b/arch/x86/include/asm/sparsemem.h | 3 ---
> b/arch/x86/kernel/setup.c | 10 +++++++++-
> 2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff -puN arch/x86/kernel/setup.c~iomem_resource_end arch/x86/kernel/setup.c
> --- a/arch/x86/kernel/setup.c~iomem_resource_end 2024-02-22 10:08:51.048554948 -0800
> +++ b/arch/x86/kernel/setup.c 2024-02-22 10:21:04.485531464 -0800
> @@ -51,6 +51,7 @@
> #include <asm/pci-direct.h>
> #include <asm/prom.h>
> #include <asm/proto.h>
> +#include <asm/sparsemem.h>
> #include <asm/thermal.h>
> #include <asm/unwind.h>
> #include <asm/vsyscall.h>
> @@ -813,7 +814,14 @@ void __init setup_arch(char **cmdline_p)
> */
> early_reserve_memory();
>
> - iomem_resource.end = (1ULL << x86_phys_bits()) - 1;
> + /*
> + * This was too big before. It ended up getting MAX_PHYSMEM_BITS
> + * even if .x86_phys_bits was eventually lowered below that.
> + * But that was evidently harmless, so leave it too big, but
> + * set it explicitly to MAX_PHYSMEM_BITS instead of taking a
> + * trip through .x86_phys_bits.
> + */
> + iomem_resource.end = (1ULL << MAX_PHYSMEM_BITS) - 1;

Paolo's patchset to move MKTME keyid bits detection to early_cpu_init() was
merged to tip:x86/urgent, so looks it will land to Linus's tree before this
series:

https://lore.kernel.org/lkml/eff34df2-fdc1-4ee0-bb8d-90da386b7cb6@intel.com/T/

Paplo's series actually moves the reduction of x86_phys_bits before setting the
iomem_resource.end here, so after rebasing the changelog/comment seems don't
apply anymore.

Perhaps we can get rid of this patch and just set iomem_resource.end based on
x86_phys_bits()?