[PATCHv3 2/5] x86/boot/compressed/64: Print error if 5-level paging is not supported

Kirill A. Shutemov
2017-12-04T12:41:43Z

We cannot proceed booting if the machine doesn't support the paging mode
kernel was compiled for.

Getting error the usual way -- via validate_cpu() -- is not going to
work. We need to enable appropriate paging mode before that, otherwise
kernel would triple-fault during KASLR setup.

This code will go away once we get support for boot-time switching
between paging modes.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org> [4.14+]
---
arch/x86/boot/compressed/misc.c | 16 ++++++++++++++++
arch/x86/boot/compressed/pgtable_64.c | 2 +-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index b50c42455e25..f7f8d9f76e15 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -169,6 +169,16 @@ void __puthex(unsigned long value)
}
}

+static int l5_supported(void)
+{
+ /* Check if leaf 7 is supported. */
+ if (native_cpuid_eax(0) < 7)
+ return 0;
+
+ /* Check if la57 is supported. */
+ return native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31));
+}
+
#if CONFIG_X86_NEED_RELOCS
static void handle_relocations(void *output, unsigned long output_len,
unsigned long virt_addr)
@@ -362,6 +372,12 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
console_init();
debug_putstr("early console in extract_kernel\n");

+ if (IS_ENABLED(CONFIG_X86_5LEVEL) && !l5_supported()) {
+ error("This linux kernel as configured requires 5-level paging\n"
+ "This CPU does not support the required 'cr4.la57' feature\n"
+ "Unable to boot - please use a kernel appropriate for your CPU\n");
+ }
+
free_mem_ptr = heap; /* Heap */
free_mem_end_ptr = heap + BOOT_HEAP_SIZE;

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index eed3a2c3b577..7bcf03b376da 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -2,7 +2,7 @@

int l5_paging_required(void)
{
- /* Check i leaf 7 is supported. */
+ /* Check if leaf 7 is supported. */
if (native_cpuid_eax(0) < 7)
return 0;

--
2.15.0