linux-kernel - [RFC v2 22/32] x86/boot: Avoid #VE during compressed boot for TDX platforms

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Date:   Mon, 26 Apr 2021 11:01:49 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: [RFC v2 22/32] x86/boot: Avoid #VE during compressed boot for TDX platforms

From: Sean Christopherson <sean.j.christopherson@...el.com>

Avoid operations which will inject #VE during compressed
boot, which is obviously fatal for TDX platforms.

Details are,

 1. TDX module injects #VE if a TDX guest attempts to write
    EFER. So skip the WRMSR to set EFER.LME=1 if it's already
    set. TDX also forces EFER.LME=1, i.e. the branch will always
    be taken and thus the #VE avoided.

 2. TDX module also injects a #VE if the guest attempts to clear
    CR0.NE. Ensure CR0.NE is set when loading CR0 during compressed
    boot. The Setting CR0.NE should be a nop on all CPUs that
    support 64-bit mode.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---
 arch/x86/boot/compressed/head_64.S | 5 +++--
 arch/x86/boot/compressed/pgtable.h | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index e94874f4bbc1..37c2f37d4a0d 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -616,8 +616,9 @@ SYM_CODE_START(trampoline_32bit_src)
 	movl	$MSR_EFER, %ecx
 	rdmsr
 	btsl	$_EFER_LME, %eax
+	jc	1f
 	wrmsr
-	popl	%edx
+1:	popl	%edx
 	popl	%ecx
 
 	/* Enable PAE and LA57 (if required) paging modes */
@@ -636,7 +637,7 @@ SYM_CODE_START(trampoline_32bit_src)
 	pushl	%eax
 
 	/* Enable paging again */
-	movl	$(X86_CR0_PG | X86_CR0_PE), %eax
+	movl	$(X86_CR0_PG | X86_CR0_NE | X86_CR0_PE), %eax
 	movl	%eax, %cr0
 
 	lret
diff --git a/arch/x86/boot/compressed/pgtable.h b/arch/x86/boot/compressed/pgtable.h
index 6ff7e81b5628..cc9b2529a086 100644
--- a/arch/x86/boot/compressed/pgtable.h
+++ b/arch/x86/boot/compressed/pgtable.h
@@ -6,7 +6,7 @@
 #define TRAMPOLINE_32BIT_PGTABLE_OFFSET	0
 
 #define TRAMPOLINE_32BIT_CODE_OFFSET	PAGE_SIZE
-#define TRAMPOLINE_32BIT_CODE_SIZE	0x70
+#define TRAMPOLINE_32BIT_CODE_SIZE	0x80
 
 #define TRAMPOLINE_32BIT_STACK_END	TRAMPOLINE_32BIT_SIZE
 
-- 
2.25.1