Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCHv2 13/29] x86/tdx: Add port I/O emulation | Date | Mon, 24 Jan 2022 18:01:59 +0300 |
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From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
TDX hypervisors cannot emulate instructions directly. This includes port I/O which is normally emulated in the hypervisor. All port I/O instructions inside TDX trigger the #VE exception in the guest and would be normally emulated there.
Use a hypercall to emulate port I/O. Extend the tdx_handle_virt_exception() and add support to handle the #VE due to port I/O instructions.
String I/O operations are not supported in TDX. Unroll them by declaring CC_ATTR_GUEST_UNROLL_STRING_IO confidential computing attribute.
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Reviewed-by: Andi Kleen <ak@linux.intel.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/kernel/cc_platform.c | 3 +++ arch/x86/kernel/tdx.c | 48 +++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+)
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c index c72b3919bca9..8da246ab4339 100644 --- a/arch/x86/kernel/cc_platform.c +++ b/arch/x86/kernel/cc_platform.c @@ -17,6 +17,9 @@ static bool intel_cc_platform_has(enum cc_attr attr) { + if (attr == CC_ATTR_GUEST_UNROLL_STRING_IO) + return true; + return false; } diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c index 8e630eeb765d..e73af22a4c11 100644 --- a/arch/x86/kernel/tdx.c +++ b/arch/x86/kernel/tdx.c @@ -13,6 +13,12 @@ /* TDX module Call Leaf IDs */ #define TDX_GET_VEINFO 3 +/* See Exit Qualification for I/O Instructions in VMX documentation */ +#define VE_IS_IO_IN(exit_qual) (((exit_qual) & 8) ? 1 : 0) +#define VE_GET_IO_SIZE(exit_qual) (((exit_qual) & 7) + 1) +#define VE_GET_PORT_NUM(exit_qual) ((exit_qual) >> 16) +#define VE_IS_IO_STRING(exit_qual) ((exit_qual) & 16 ? 1 : 0) + static bool tdx_guest_detected __ro_after_init; /* @@ -257,6 +263,45 @@ static int tdx_handle_mmio(struct pt_regs *regs, struct ve_info *ve) return insn.length; } +/* + * Emulate I/O using hypercall. + * + * Assumes the IO instruction was using ax, which is enforced + * by the standard io.h macros. + * + * Return True on success or False on failure. + */ +static bool tdx_handle_io(struct pt_regs *regs, u32 exit_qual) +{ + struct tdx_hypercall_output out; + int size, port, ret; + u64 mask; + bool in; + + if (VE_IS_IO_STRING(exit_qual)) + return false; + + in = VE_IS_IO_IN(exit_qual); + size = VE_GET_IO_SIZE(exit_qual); + port = VE_GET_PORT_NUM(exit_qual); + mask = GENMASK(BITS_PER_BYTE * size, 0); + + /* + * Emulate the I/O read/write via hypercall. More info about + * ABI can be found in TDX Guest-Host-Communication Interface + * (GHCI) sec titled "TDG.VP.VMCALL<Instruction.IO>". + */ + ret = _tdx_hypercall(EXIT_REASON_IO_INSTRUCTION, size, !in, port, + in ? 0 : regs->ax, &out); + if (!in) + return !ret; + + regs->ax &= ~mask; + regs->ax |= ret ? UINT_MAX : out.r11 & mask; + + return !ret; +} + bool tdx_get_ve_info(struct ve_info *ve) { struct tdx_module_output out; @@ -333,6 +378,9 @@ static bool tdx_virt_exception_kernel(struct pt_regs *regs, struct ve_info *ve) if (!ret) pr_warn_once("MMIO failed\n"); break; + case EXIT_REASON_IO_INSTRUCTION: + ret = tdx_handle_io(regs, ve->exit_qual); + break; default: pr_warn("Unexpected #VE: %lld\n", ve->exit_reason); break; -- 2.34.1
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