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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
        Sean Christopherson <seanjc@google.com>,
        Sagi Shahar <sagis@google.com>
Subject: [RFC PATCH v6 064/104] KVM: TDX: Add helper assembly function to TDX vcpu
Date:   Thu,  5 May 2022 11:14:58 -0700
Message-Id: <f40b7827026d65963fea84d4af78cb1cbca85149.1651774250.git.isaku.yamahata@intel.com>
In-Reply-To: <cover.1651774250.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

TDX defines an API to run TDX vcpu with its own ABI.  Define an assembly
helper function to run TDX vcpu to hide the special ABI so that C code can
call it with function call ABI.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/vmx/vmenter.S | 146 +++++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 435c187927c4..f655bcca0e93 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -2,6 +2,7 @@
 #include <linux/linkage.h>
 #include <asm/asm.h>
 #include <asm/bitsperlong.h>
+#include <asm/errno.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/nospec-branch.h>
 #include <asm/segment.h>
@@ -28,6 +29,13 @@
 #define VCPU_R15	__VCPU_REGS_R15 * WORD_SIZE
 #endif
 
+#ifdef CONFIG_INTEL_TDX_HOST
+#define TDENTER 		0
+#define EXIT_REASON_TDCALL	77
+#define TDENTER_ERROR_BIT	63
+#define seamcall		.byte 0x66,0x0f,0x01,0xcf
+#endif
+
 .section .noinstr.text, "ax"
 
 /**
@@ -328,3 +336,141 @@ SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff)
 	pop %_ASM_BP
 	RET
 SYM_FUNC_END(vmx_do_interrupt_nmi_irqoff)
+
+#ifdef CONFIG_INTEL_TDX_HOST
+
+.pushsection .noinstr.text, "ax"
+
+/**
+ * __tdx_vcpu_run - Call SEAMCALL(TDENTER) to run a TD vcpu
+ * @tdvpr:	physical address of TDVPR
+ * @regs:	void * (to registers of TDVCPU)
+ * @gpr_mask:	non-zero if guest registers need to be loaded prior to TDENTER
+ *
+ * Returns:
+ *	TD-Exit Reason
+ *
+ * Note: KVM doesn't support using XMM in its hypercalls, it's the HyperV
+ *	 code's responsibility to save/restore XMM registers on TDVMCALL.
+ */
+SYM_FUNC_START(__tdx_vcpu_run)
+	push %rbp
+	mov  %rsp, %rbp
+
+	push %r15
+	push %r14
+	push %r13
+	push %r12
+	push %rbx
+
+	/* Save @regs, which is needed after TDENTER to capture output. */
+	push %rsi
+
+	/* Load @tdvpr to RCX */
+	mov %rdi, %rcx
+
+	/* No need to load guest GPRs if the last exit wasn't a TDVMCALL. */
+	test %dx, %dx
+	je 1f
+
+	/* Load @regs to RAX, which will be clobbered with $TDENTER anyways. */
+	mov %rsi, %rax
+
+	mov VCPU_RBX(%rax), %rbx
+	mov VCPU_RDX(%rax), %rdx
+	mov VCPU_RBP(%rax), %rbp
+	mov VCPU_RSI(%rax), %rsi
+	mov VCPU_RDI(%rax), %rdi
+
+	mov VCPU_R8 (%rax),  %r8
+	mov VCPU_R9 (%rax),  %r9
+	mov VCPU_R10(%rax), %r10
+	mov VCPU_R11(%rax), %r11
+	mov VCPU_R12(%rax), %r12
+	mov VCPU_R13(%rax), %r13
+	mov VCPU_R14(%rax), %r14
+	mov VCPU_R15(%rax), %r15
+
+	/*  Load TDENTER to RAX.  This kills the @regs pointer! */
+1:	mov $TDENTER, %rax
+
+2:	seamcall
+
+	/* Skip to the exit path if TDENTER failed. */
+	bt $TDENTER_ERROR_BIT, %rax
+	jc 4f
+
+	/* Temporarily save the TD-Exit reason. */
+	push %rax
+
+	/* check if TD-exit due to TDVMCALL */
+	cmp $EXIT_REASON_TDCALL, %ax
+
+	/* Reload @regs to RAX. */
+	mov 8(%rsp), %rax
+
+	/* Jump on non-TDVMCALL */
+	jne 3f
+
+	/* Save all output from SEAMCALL(TDENTER) */
+	mov %rbx, VCPU_RBX(%rax)
+	mov %rbp, VCPU_RBP(%rax)
+	mov %rsi, VCPU_RSI(%rax)
+	mov %rdi, VCPU_RDI(%rax)
+	mov %r10, VCPU_R10(%rax)
+	mov %r11, VCPU_R11(%rax)
+	mov %r12, VCPU_R12(%rax)
+	mov %r13, VCPU_R13(%rax)
+	mov %r14, VCPU_R14(%rax)
+	mov %r15, VCPU_R15(%rax)
+
+3:	mov %rcx, VCPU_RCX(%rax)
+	mov %rdx, VCPU_RDX(%rax)
+	mov %r8,  VCPU_R8 (%rax)
+	mov %r9,  VCPU_R9 (%rax)
+
+	/*
+	 * Clear all general purpose registers except RSP and RAX to prevent
+	 * speculative use of the guest's values.
+	 */
+	xor %rbx, %rbx
+	xor %rcx, %rcx
+	xor %rdx, %rdx
+	xor %rsi, %rsi
+	xor %rdi, %rdi
+	xor %rbp, %rbp
+	xor %r8,  %r8
+	xor %r9,  %r9
+	xor %r10, %r10
+	xor %r11, %r11
+	xor %r12, %r12
+	xor %r13, %r13
+	xor %r14, %r14
+	xor %r15, %r15
+
+	/* Restore the TD-Exit reason to RAX for return. */
+	pop %rax
+
+	/* "POP" @regs. */
+4:	add $8, %rsp
+	pop %rbx
+	pop %r12
+	pop %r13
+	pop %r14
+	pop %r15
+
+	pop %rbp
+	ret
+
+5:	cmpb $0, kvm_rebooting
+	je 6f
+	mov $-EFAULT, %rax
+	jmp 4b
+6:	ud2
+	_ASM_EXTABLE(2b, 5b)
+
+SYM_FUNC_END(__tdx_vcpu_run)
+
+.popsection
+
+#endif
-- 
2.25.1