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SubjectRe: [PATCH 25/62] x86/head/64: Install boot GDT
On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@8bytes.org> wrote:
>
> From: Joerg Roedel <jroedel@suse.de>
>
> Handling exceptions during boot requires a working GDT. The kernel GDT
> is not yet ready for use, so install a temporary boot GDT.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/kernel/head_64.S | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 4bbc770af632..5a3cde971cb7 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -72,6 +72,20 @@ SYM_CODE_START_NOALIGN(startup_64)
> /* Set up the stack for verify_cpu(), similar to initial_stack below */
> leaq (__end_init_task - SIZEOF_PTREGS)(%rip), %rsp
>
> + /* Setup boot GDT descriptor and load boot GDT */
> + leaq boot_gdt(%rip), %rax
> + movq %rax, boot_gdt_base(%rip)
> + lgdt boot_gdt_descr(%rip)
> +
> + /* GDT loaded - switch to __KERNEL_CS so IRET works reliably */
> + pushq $__KERNEL_CS
> + leaq .Lon_kernel_cs(%rip), %rax
> + pushq %rax
> + lretq
> +
> +.Lon_kernel_cs:
> + UNWIND_HINT_EMPTY

I would suggest fixing at least SS as well.

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