Thanks Arvind, this is good stuff.
On Thu, 30 Jan 2020 at 21:04, Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote:
>
> For the 64-bit kernel, we do not need to setup a GDT in efi_main, as the
> next step in the boot, startup_64, will set one up.
>
This seems obvious, but I need a nod from Ingo or Boris before I can take this.
> This series factors out the GDT setup into a separate function and
> restricts it to the 32-bit kernel. The memory allocation for the GDT is
> also changed from allocating a full page via efi_alloc_low to the
> required space (32 bytes) from alloc_pool boot service.
>
Can we go all the way and simply make this
if (IS_ENABLED(CONFIG_X64_32)) {
static const struct desc_struct desc[] __aligned(8) = {
{}, /* The first GDT is a dummy. */
{}, /* Second entry is unused on 32-bit */
GDT_ENTRY_INIT(0xa09b, 0, 0xfffff), /* __KERNEL_CS */
GDT_ENTRY_INIT(0xc093, 0, 0xfffff), /* __KERNEL_DS */
};
struct desc_ptr gdt = { sizeof(desc) - 1, (unsigned long)desc };
native_load_gdt(&gdt);
}
(and drop the #defines from eboot.h that we no longer use)
> The final two patches are doc fixes to clarify that the 32-bit EFI
> handover entry point also requires segments/GDT to be setup, and that
> for 64-bit mode we don't have any special segment requirements (the
> 64-bit doc currently is just a copy of the 32-bit doc which isn't
> right).
>
> Arvind Sankar (8):
> efi/x86: Use C wrapper instead of inline assembly
> efi/x86: Allocate the GDT pointer on the stack
> efi/x86: Factor GDT setup code into a function
Given the above, I don't think we need the separate function, but if
we do, please drop the 64-bit code first, otherwise there is much more
churn than necessary.
> efi/x86: Only setup the GDT for 32-bit kernel
> efi/x86: Allocate only the required 32 bytes for the GDT
> efi/x86: Change __KERNEL_{CS,DS} to __BOOT_{CS,DS}
> Documentation/x86/boot: Clarify segment requirements for EFI handover
> Documentation/x86/boot: Correct segment requirements for 64-bit boot
>
> Documentation/x86/boot.rst | 15 +-
> arch/x86/boot/compressed/eboot.c | 174 ++++++++++--------------
> arch/x86/boot/compressed/efi_thunk_64.S | 4 +-
> 3 files changed, 85 insertions(+), 108 deletions(-)
>
> --
> 2.24.1
>
