On Wed, 18 May, at 02:11:41PM, Alex Thorlton wrote:
> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
> index f310f0b..6643f9b 100644
> --- a/arch/x86/include/asm/efi.h
> +++ b/arch/x86/include/asm/efi.h
> @@ -68,6 +68,52 @@ struct efi_scratch {
> u64 phys_stack;
> } __packed;
>
> +#ifdef CONFIG_EFI_MIXED
> +extern efi_status_t efi64_thunk(u32, ...);
> +
> +#define runtime_service32(func)
> \
> +({ \
> + u32 table = (u32)(unsigned long)efi.systab; \
> + u32 *rt, *___f; \
> + \
> + rt = (u32 *)(table + offsetof(efi_system_table_32_t, runtime)); \
> + ___f = (u32 *)(*rt + offsetof(efi_runtime_services_32_t, func)); \
> + *___f; \
> +})
> +
> +/*
> + * Switch to the EFI page tables early so that we can access the 1:1
> + * runtime services mappings which are not mapped in any other page
> + * tables. This function must be called before runtime_service32().
> + *
> + * Also, disable interrupts because the IDT points to 64-bit handlers,
> + * which aren't going to function correctly when we switch to 32-bit.
> + */
> +#define arch_efi_call_virt_setup() \
> +({ \
> + efi_sync_low_kernel_mappings(); \
> + local_irq_save(flags); \
> + \
> + efi_scratch.prev_cr3 = read_cr3(); \
> + write_cr3((unsigned long)efi_scratch.efi_pgt); \
> + __flush_tlb_all(); \
> +})
> +
> +#define arch_efi_call_virt(p, f, ...)
> \
> +({ \
> + u32 func = runtime_service32(f); \
> + efi64_thunk(func, __VA_ARGS__); \
> +})
> +
This isn't correct because you're turning the runtime decision of
whether we're executing the thunking code into a build time one.
Users can enable CONFIG_EFI_MIXED in their builds but never actually
run that kernel on a mixed mode machine. One of the original design
intentions behind CONFIG_EFI_MIXED was that you can (and should!) turn
it on because it has no effect unless you run it on a machine with
32-bit EFI.
The switch to the thunk layer is done in efi_thunk_runtime_setup().
As a real world example of this, the openSUSE x86_64 kernel config has
CONFIG_EFI_MIXED enabled out of the box.
The thunk code should be able to reuse the regular x86_64
arch_efi_call_virt_setup() and arch_efi_call_virt_teardown(), since,
a. We can also disable preemption without issue
b. We can disable/reenable interrupts around those existing wrappers
c. The "if (efi_scratch.use_pgd)" check is missing because we
*always* use the EFI pgtables for mixed mode, it's a requirement
Would something like this work instead? It's not as neat as your
suggestion but it's a damn sight better than what we have today.
---
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 6e7242be1c87..b976084e56ef 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -469,18 +469,13 @@ extern efi_status_t efi64_thunk(u32, ...);
unsigned long flags; \
u32 func; \
\
- efi_sync_low_kernel_mappings(); \
local_irq_save(flags); \
- \
- efi_scratch.prev_cr3 = read_cr3(); \
- write_cr3((unsigned long)efi_scratch.efi_pgt); \
- __flush_tlb_all(); \
+ arch_efi_call_virt_setup(); \
\
func = runtime_service32(f); \
__s = efi64_thunk(func, __VA_ARGS__); \
\
- write_cr3(efi_scratch.prev_cr3); \
- __flush_tlb_all(); \
+ arch_efi_call_virt_teardown(); \
local_irq_restore(flags); \
\
__s; \
