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    Subject[PATCHv2 2/4] x86/boot/compressed/64: Detect and handle 5-level paging at boot-time
    Date
    This patch prepare decompression code to boot-time switching between 4-
    and 5-level paging.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    arch/x86/boot/compressed/Makefile | 1 +
    arch/x86/boot/compressed/head_64.S | 16 ++++++++++++----
    arch/x86/boot/compressed/pgtable_64.c | 18 ++++++++++++++++++
    3 files changed, 31 insertions(+), 4 deletions(-)
    create mode 100644 arch/x86/boot/compressed/pgtable_64.c

    diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    index ae0be0b923e1..1f734cd98fd3 100644
    --- a/arch/x86/boot/compressed/Makefile
    +++ b/arch/x86/boot/compressed/Makefile
    @@ -80,6 +80,7 @@ vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
    ifdef CONFIG_X86_64
    vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr_64.o
    vmlinux-objs-y += $(obj)/mem_encrypt.o
    + vmlinux-objs-y += $(obj)/pgtable_64.o
    endif

    $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
    diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
    index 20919b4f3133..fc313e29fe2c 100644
    --- a/arch/x86/boot/compressed/head_64.S
    +++ b/arch/x86/boot/compressed/head_64.S
    @@ -305,10 +305,18 @@ ENTRY(startup_64)
    leaq boot_stack_end(%rbx), %rsp

    #ifdef CONFIG_X86_5LEVEL
    - /* Check if 5-level paging has already enabled */
    - movq %cr4, %rax
    - testl $X86_CR4_LA57, %eax
    - jnz lvl5
    + /*
    + * Check if we need to enable 5-level paging.
    + * RSI holds real mode data and need to be preserved across
    + * a function call.
    + */
    + pushq %rsi
    + call l5_paging_required
    + popq %rsi
    +
    + /* If l5_paging_required() returned zero, we're done here. */
    + cmpq $0, %rax
    + je lvl5

    /*
    * At this point we are in long mode with 4-level paging enabled,
    diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
    new file mode 100644
    index 000000000000..eed3a2c3b577
    --- /dev/null
    +++ b/arch/x86/boot/compressed/pgtable_64.c
    @@ -0,0 +1,18 @@
    +#include <asm/processor.h>
    +
    +int l5_paging_required(void)
    +{
    + /* Check i leaf 7 is supported. */
    + if (native_cpuid_eax(0) < 7)
    + return 0;
    +
    + /* Check if la57 is supported. */
    + if (!(native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31))))
    + return 0;
    +
    + /* Check if 5-level paging has already been enabled. */
    + if (native_read_cr4() & X86_CR4_LA57)
    + return 0;
    +
    + return 1;
    +}
    --
    2.14.2
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