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Subject[PATCH 4.4 04/27] x86/efi: Hoist page table switching code into efi_call_virt()
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matt Fleming <matt@codeblueprint.co.uk>

commit c9f2a9a65e4855b74d92cdad688f6ee4a1a323ff upstream.

This change is a prerequisite for pending patches that switch to
a dedicated EFI page table, instead of using 'trampoline_pgd'
which shares PGD entries with 'swapper_pg_dir'. The pending
patches make it impossible to dereference the runtime service
function pointer without first switching %cr3.

It's true that we now have duplicated switching code in
efi_call_virt() and efi_call_phys_{prolog,epilog}() but we are
sacrificing code duplication for a little more clarity and the
ease of writing the page table switching code in C instead of
asm.

Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1448658575-17029-5-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "Ghannam, Yazen" <Yazen.Ghannam@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/efi.h | 25 ++++++++++++++++++++
arch/x86/platform/efi/efi_64.c | 24 +++++++++-----------
arch/x86/platform/efi/efi_stub_64.S | 43 ------------------------------------
3 files changed, 36 insertions(+), 56 deletions(-)

--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -3,6 +3,7 @@

#include <asm/fpu/api.h>
#include <asm/pgtable.h>
+#include <asm/tlb.h>

/*
* We map the EFI regions needed for runtime services non-contiguously,
@@ -64,6 +65,17 @@ extern u64 asmlinkage efi_call(void *fp,

#define efi_call_phys(f, args...) efi_call((f), args)

+/*
+ * Scratch space used for switching the pagetable in the EFI stub
+ */
+struct efi_scratch {
+ u64 r15;
+ u64 prev_cr3;
+ pgd_t *efi_pgt;
+ bool use_pgd;
+ u64 phys_stack;
+} __packed;
+
#define efi_call_virt(f, ...) \
({ \
efi_status_t __s; \
@@ -71,7 +83,20 @@ extern u64 asmlinkage efi_call(void *fp,
efi_sync_low_kernel_mappings(); \
preempt_disable(); \
__kernel_fpu_begin(); \
+ \
+ if (efi_scratch.use_pgd) { \
+ efi_scratch.prev_cr3 = read_cr3(); \
+ write_cr3((unsigned long)efi_scratch.efi_pgt); \
+ __flush_tlb_all(); \
+ } \
+ \
__s = efi_call((void *)efi.systab->runtime->f, __VA_ARGS__); \
+ \
+ if (efi_scratch.use_pgd) { \
+ write_cr3(efi_scratch.prev_cr3); \
+ __flush_tlb_all(); \
+ } \
+ \
__kernel_fpu_end(); \
preempt_enable(); \
__s; \
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -47,16 +47,7 @@
*/
static u64 efi_va = EFI_VA_START;

-/*
- * Scratch space used for switching the pagetable in the EFI stub
- */
-struct efi_scratch {
- u64 r15;
- u64 prev_cr3;
- pgd_t *efi_pgt;
- bool use_pgd;
- u64 phys_stack;
-} __packed;
+struct efi_scratch efi_scratch;

static void __init early_code_mapping_set_exec(int executable)
{
@@ -83,8 +74,11 @@ pgd_t * __init efi_call_phys_prolog(void
int pgd;
int n_pgds;

- if (!efi_enabled(EFI_OLD_MEMMAP))
- return NULL;
+ if (!efi_enabled(EFI_OLD_MEMMAP)) {
+ save_pgd = (pgd_t *)read_cr3();
+ write_cr3((unsigned long)efi_scratch.efi_pgt);
+ goto out;
+ }

early_code_mapping_set_exec(1);

@@ -96,6 +90,7 @@ pgd_t * __init efi_call_phys_prolog(void
vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
}
+out:
__flush_tlb_all();

return save_pgd;
@@ -109,8 +104,11 @@ void __init efi_call_phys_epilog(pgd_t *
int pgd_idx;
int nr_pgds;

- if (!save_pgd)
+ if (!efi_enabled(EFI_OLD_MEMMAP)) {
+ write_cr3((unsigned long)save_pgd);
+ __flush_tlb_all();
return;
+ }

nr_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE);

--- a/arch/x86/platform/efi/efi_stub_64.S
+++ b/arch/x86/platform/efi/efi_stub_64.S
@@ -38,41 +38,6 @@
mov %rsi, %cr0; \
mov (%rsp), %rsp

- /* stolen from gcc */
- .macro FLUSH_TLB_ALL
- movq %r15, efi_scratch(%rip)
- movq %r14, efi_scratch+8(%rip)
- movq %cr4, %r15
- movq %r15, %r14
- andb $0x7f, %r14b
- movq %r14, %cr4
- movq %r15, %cr4
- movq efi_scratch+8(%rip), %r14
- movq efi_scratch(%rip), %r15
- .endm
-
- .macro SWITCH_PGT
- cmpb $0, efi_scratch+24(%rip)
- je 1f
- movq %r15, efi_scratch(%rip) # r15
- # save previous CR3
- movq %cr3, %r15
- movq %r15, efi_scratch+8(%rip) # prev_cr3
- movq efi_scratch+16(%rip), %r15 # EFI pgt
- movq %r15, %cr3
- 1:
- .endm
-
- .macro RESTORE_PGT
- cmpb $0, efi_scratch+24(%rip)
- je 2f
- movq efi_scratch+8(%rip), %r15
- movq %r15, %cr3
- movq efi_scratch(%rip), %r15
- FLUSH_TLB_ALL
- 2:
- .endm
-
ENTRY(efi_call)
SAVE_XMM
mov (%rsp), %rax
@@ -83,16 +48,8 @@ ENTRY(efi_call)
mov %r8, %r9
mov %rcx, %r8
mov %rsi, %rcx
- SWITCH_PGT
call *%rdi
- RESTORE_PGT
addq $48, %rsp
RESTORE_XMM
ret
ENDPROC(efi_call)
-
- .data
-ENTRY(efi_scratch)
- .fill 3,8,0
- .byte 0
- .quad 0

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