Commit b677dfae authored Jan 03, 2019 by Wei Huang Committed by Thomas Gleixner Jan 29, 2019

x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline before returning to long mode



In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM
when the hypervsior detects that the guest sets CR0.PG to 0. This causes
the guest OS to reboot when it tries to return from 32-bit trampoline code
because the CPU is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but
EFER.LME=0.  As a precaution, set EFER.LME=1 as part of long mode
activation procedure. This extra step won't cause any harm when Linux is
booted on a bare-metal machine.

Signed-off-by: Wei Huang <wei@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20190104054411.12489-1-wei@redhat.com

parent 00ae831d

arch/x86/boot/compressed/head_64.S

+8 −0

Original line number	Diff line number	Diff line
		@@ -600,6 +600,14 @@ ENTRY(trampoline_32bit_src)
		leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax
		movl %eax, %cr3
		3:
		/* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */
		pushl %ecx
		movl $MSR_EFER, %ecx
		rdmsr
		btsl $_EFER_LME, %eax
		wrmsr
		popl %ecx

		/* Enable PAE and LA57 (if required) paging modes */
		movl $X86_CR4_PAE, %eax
		cmpl $0, %edx

arch/x86/boot/compressed/pgtable.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -6,7 +6,7 @@
		#define TRAMPOLINE_32BIT_PGTABLE_OFFSET 0

		#define TRAMPOLINE_32BIT_CODE_OFFSET PAGE_SIZE
		#define TRAMPOLINE_32BIT_CODE_SIZE 0x60
		#define TRAMPOLINE_32BIT_CODE_SIZE 0x70

		#define TRAMPOLINE_32BIT_STACK_END TRAMPOLINE_32BIT_SIZE

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