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Subject[PATCH v10 09/11] x86/tdx: Add MSR support for TDX guest
Date
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

Use hypercall to emulate MSR read/write for TDX platform.

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

RDMSR and WRMSR specification details can be found in
Guest-Host-Communication Interface (GHCI) for Intel Trust Domain
Extensions (Intel TDX) specification, sec titled "TDG.VP.
VMCALL<Instruction.RDMSR>" and "TDG.VP.VMCALL<Instruction.WRMSR>".

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>
---

Changes since v9:
* None

Changes since v8:
* Changed tdx_read_msr_safe() return type to bool.
* Changed tdx_write_msr_safe() return type to bool.
* Changed second argument of tdx_read_msr_safe() from err to val.
* Fixed compliation error due to use of tdx_is_context_switched_msr().

Changes since v7:
* Removed tdx_is_context_switched_msr() support (since the list
is incomplete).
* Added section title to spec reference.

Changes since v6:
* None

Changes since v5:
* Renamed "tdg" prefix with "tdx".
* Added comments for _tdx_hypercall() usage in MSR read/write functions.

Change since v4:
* Removed You usage from commit log.

Changes since v3:
* None

arch/x86/kernel/tdx.c | 51 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index c05e8824e5e0..7c6c84015302 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -110,6 +110,39 @@ static __cpuidle void tdx_safe_halt(void)
_tdx_halt(irq_disabled, do_sti);
}

+static bool tdx_read_msr_safe(unsigned int msr, u64 *val)
+{
+ struct tdx_hypercall_output out;
+
+ /*
+ * Emulate the MSR read via hypercall. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface
+ * (GHCI), sec titled "TDG.VP.VMCALL<Instruction.RDMSR>".
+ */
+ if (_tdx_hypercall(EXIT_REASON_MSR_READ, msr, 0, 0, 0, &out))
+ return false;
+
+ *val = out.r11;
+
+ return true;
+}
+
+static bool tdx_write_msr_safe(unsigned int msr, unsigned int low,
+ unsigned int high)
+{
+ u64 ret;
+
+ /*
+ * Emulate the MSR write via hypercall. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface
+ * (GHCI) sec titled "TDG.VP.VMCALL<Instruction.WRMSR>".
+ */
+ ret = _tdx_hypercall(EXIT_REASON_MSR_WRITE, msr, (u64)high << 32 | low,
+ 0, 0, NULL);
+
+ return ret ? false : true;
+}
+
bool tdx_get_ve_info(struct ve_info *ve)
{
struct tdx_module_output out;
@@ -141,19 +174,33 @@ bool tdx_get_ve_info(struct ve_info *ve)
bool tdx_handle_virtualization_exception(struct pt_regs *regs,
struct ve_info *ve)
{
+ bool ret = true;
+ u64 val;
+
switch (ve->exit_reason) {
case EXIT_REASON_HLT:
tdx_halt();
break;
+ case EXIT_REASON_MSR_READ:
+ ret = tdx_read_msr_safe(regs->cx, &val);
+ if (ret) {
+ regs->ax = (u32)val;
+ regs->dx = val >> 32;
+ }
+ break;
+ case EXIT_REASON_MSR_WRITE:
+ ret = tdx_write_msr_safe(regs->cx, regs->ax, regs->dx);
+ break;
default:
pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
return false;
}

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

- return true;
+ return ret;
}

void __init tdx_early_init(void)
--
2.25.1
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