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Subject[PATCH v3 10/11] x86/tdx: Add MSR support for TDX guest
Date
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

Operations on context-switched MSRs can be run natively. The rest of
MSRs should be handled through TDVMCALLs.

TDVMCALL[Instruction.RDMSR] and TDVMCALL[Instruction.WRMSR] provide
MSR oprations.

You can find RDMSR and WRMSR details in Guest-Host-Communication
Interface (GHCI) for Intel Trust Domain Extensions (Intel TDX)
specification, sec 3.10, 3.11.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
arch/x86/kernel/tdx.c | 67 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 1ce528f8fc95..a02ee45695e6 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -108,6 +108,55 @@ static __cpuidle void tdg_safe_halt(void)
BUG_ON(ret);
}

+static bool tdg_is_context_switched_msr(unsigned int msr)
+{
+ switch (msr) {
+ case MSR_EFER:
+ case MSR_IA32_CR_PAT:
+ case MSR_FS_BASE:
+ case MSR_GS_BASE:
+ case MSR_KERNEL_GS_BASE:
+ case MSR_IA32_SYSENTER_CS:
+ case MSR_IA32_SYSENTER_EIP:
+ case MSR_IA32_SYSENTER_ESP:
+ case MSR_STAR:
+ case MSR_LSTAR:
+ case MSR_SYSCALL_MASK:
+ case MSR_IA32_XSS:
+ case MSR_TSC_AUX:
+ case MSR_IA32_BNDCFGS:
+ return true;
+ }
+ return false;
+}
+
+static u64 tdg_read_msr_safe(unsigned int msr, int *err)
+{
+ u64 ret;
+ struct tdx_hypercall_output out = {0};
+
+ WARN_ON_ONCE(tdg_is_context_switched_msr(msr));
+
+ ret = _tdx_hypercall(EXIT_REASON_MSR_READ, msr, 0, 0, 0, &out);
+
+ *err = ret ? -EIO : 0;
+
+ return out.r11;
+}
+
+static int tdg_write_msr_safe(unsigned int msr, unsigned int low,
+ unsigned int high)
+{
+ u64 ret;
+
+ WARN_ON_ONCE(tdg_is_context_switched_msr(msr));
+
+ ret = _tdx_hypercall(EXIT_REASON_MSR_WRITE, msr, (u64)high << 32 | low,
+ 0, 0, NULL);
+
+ return ret ? -EIO : 0;
+}
+
unsigned long tdg_get_ve_info(struct ve_info *ve)
{
u64 ret;
@@ -134,19 +183,33 @@ unsigned long tdg_get_ve_info(struct ve_info *ve)
int tdg_handle_virtualization_exception(struct pt_regs *regs,
struct ve_info *ve)
{
+ unsigned long val;
+ int ret = 0;
+
switch (ve->exit_reason) {
case EXIT_REASON_HLT:
tdg_halt();
break;
+ case EXIT_REASON_MSR_READ:
+ val = tdg_read_msr_safe(regs->cx, (unsigned int *)&ret);
+ if (!ret) {
+ regs->ax = val & UINT_MAX;
+ regs->dx = val >> 32;
+ }
+ break;
+ case EXIT_REASON_MSR_WRITE:
+ ret = tdg_write_msr_safe(regs->cx, regs->ax, regs->dx);
+ break;
default:
pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
return -EFAULT;
}

/* After successful #VE handling, move the IP */
- regs->ip += ve->instr_len;
+ if (!ret)
+ regs->ip += ve->instr_len;

- return 0;
+ return ret;
}

void __init tdx_early_init(void)
--
2.25.1
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