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

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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
This commit is contained in:
Wei Huang 2019-01-03 23:44:11 -06:00 committed by Thomas Gleixner
parent 00ae831dfe
commit b677dfae5a
2 changed files with 9 additions and 1 deletions
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8
arch/x86/boot/compressed/head_64.S
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@ -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

2
arch/x86/boot/compressed/pgtable.h
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@ -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