From: Sean Christopherson <sean.j.christopher...@intel.com> Skip writing EFER during secondary_startup_64() if the current value is also the desired value. This avoids a #VE when running as a TDX guest, as the TDX-Module does not allow writes to EFER (even when writing the current, fixed value).
Also, preserve CR4.MCE instead of clearing it during boot to avoid a #VE when running as a TDX guest. The TDX-Module (effectively part of the hypervisor) requires CR4.MCE to be set at all times and injects a #VE if the guest attempts to clear CR4.MCE. Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com> Reviewed-by: Andi Kleen <a...@linux.intel.com> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppusw...@linux.intel.com> --- arch/x86/boot/compressed/head_64.S | 5 ++++- arch/x86/kernel/head_64.S | 13 +++++++++++-- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 37c2f37d4a0d..2d79e5f97360 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -622,7 +622,10 @@ SYM_CODE_START(trampoline_32bit_src) popl %ecx /* Enable PAE and LA57 (if required) paging modes */ - movl $X86_CR4_PAE, %eax + movl %cr4, %eax + /* Clearing CR4.MCE will #VE on TDX guests. Leave it alone. */ + andl $X86_CR4_MCE, %eax + orl $X86_CR4_PAE, %eax testl %edx, %edx jz 1f orl $X86_CR4_LA57, %eax diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 04bddaaba8e2..92c77cf75542 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -141,7 +141,10 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) 1: /* Enable PAE mode, PGE and LA57 */ - movl $(X86_CR4_PAE | X86_CR4_PGE), %ecx + movq %cr4, %rcx + /* Clearing CR4.MCE will #VE on TDX guests. Leave it alone. */ + andl $X86_CR4_MCE, %ecx + orl $(X86_CR4_PAE | X86_CR4_PGE), %ecx #ifdef CONFIG_X86_5LEVEL testl $1, __pgtable_l5_enabled(%rip) jz 1f @@ -229,13 +232,19 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) /* Setup EFER (Extended Feature Enable Register) */ movl $MSR_EFER, %ecx rdmsr + movl %eax, %edx btsl $_EFER_SCE, %eax /* Enable System Call */ btl $20,%edi /* No Execute supported? */ jnc 1f btsl $_EFER_NX, %eax btsq $_PAGE_BIT_NX,early_pmd_flags(%rip) -1: wrmsr /* Make changes effective */ + /* Skip the WRMSR if the current value matches the desired value. */ +1: cmpl %edx, %eax + je 1f + xor %edx, %edx + wrmsr /* Make changes effective */ +1: /* Setup cr0 */ movl $CR0_STATE, %eax /* Make changes effective */ -- 2.25.1