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Prekernel: Map entire 4GiB space

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Prekernel code currently assumes that mapping until MAX_KERNEL_SIZE
is enough to make the modules accessible. GRUB tries to load as low
as possible but higher than 1 MiB. Hence this is usually true.
However on EFI some ranges may already be used by boot services and
GRUB tries to avoid them if possible. This pushes modules higher.
The simplest solution is to map entire 4 GiB space.
As an additional benefit it makes the framebuffer accessible that
can be used for the debugging.
This commit is contained in:
Vladimir Serbinenko 2023-07-22 16:51:44 +02:00 committed by Andrew Kaster
parent 31ff752a10
commit 982ce17927
1 changed files with 23 additions and 7 deletions
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30
Kernel/Prekernel/boot.S
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@ -24,7 +24,7 @@ boot_pdpt:
.skip 4096
.global boot_pd0
boot_pd0:
.skip 4096
.skip (4096 * 4)
.global boot_pd0_pts
boot_pd0_pts:
.skip 4096 * (MAX_KERNEL_SIZE >> 21)
@ -65,10 +65,10 @@ pml4t:
pdpt
0: boot_pd0 (0-1GB)
1: n/a (1-2GB)
2: n/a (2-3GB)
3: n/a (3-4GB)
0: boot_pd0 (0-1GB)
1: boot_pd0 + 4096 (1-2GB)
2: boot_pd0 + 4096 * 2 (2-3GB)
3: boot_pd0 + 4096 * 3 (3-4GB)
boot_pd0 : 512 PDEs
@ -421,13 +421,16 @@ long_mode_supported:
xorl %eax, %eax
rep stosl
/* set up pdpt[0] and pdpt[3] */
/* set up pdpt[0]..pdpt[3] */
movl $boot_pdpt, %edi
movl $(boot_pd0 + 3), 0(%edi)
movl $(boot_pd0 + 4096 + 3), 8(%edi)
movl $(boot_pd0 + 4096 * 2 + 3), 16(%edi)
movl $(boot_pd0 + 4096 * 3 + 3), 24(%edi)
/* clear pd0 */
movl $boot_pd0, %edi
movl $1024, %ecx
movl $4096, %ecx
xorl %eax, %eax
rep stosl
@ -463,6 +466,19 @@ long_mode_supported:
addl $4096, %eax
loop 1b
/* Map the rest with 2MiB pages */
/* add boot_pd0_pts to boot_pd0 */
movl $(2048 - (MAX_KERNEL_SIZE >> 21)), %ecx
movl $(boot_pd0 + (MAX_KERNEL_SIZE >> 21) * 8), %edi
/* R/W + Present + 2 MiB */
movl $(MAX_KERNEL_SIZE | 0x83), %eax
1:
movl %eax, 0(%edi)
addl $8, %edi
addl $(1 << 21), %eax
loop 1b
/* point CR3 to PML4T */
movl $boot_pml4t, %eax