Messages in this thread Patch in this message | | | From | Kai Huang <> | Subject | [PATCH v3 12/12] x86/virt/tdx: Adjust 'struct tdx_module_args' to use x86 "register index" layout | Date | Wed, 26 Jul 2023 23:25:14 +1200 |
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For TDX guest, KVM needs to call __seamcall_saved_ret() to make the TDH.VP.ENTER SEAMCALL to enter the guest, possibly taking all registers in 'struct tdx_module_args' as input/output.
KVM caches guest's GPRs in 'kvm_vcpu_arch::regs[]', which follows the "register index" hardware layout of x86 GPRs. On the other hand, the __seamcall_saved_ret() takes the pointer of 'struct tdx_module_args' as argument, thus there's a mismatch.
KVM could choose to copy input registers from 'vcpu::regs[]' to a 'struct tdx_module_args' and use that as argument to make the SEAMCALL, but such memory copy isn't desired and should be avoided if possible.
It's not feasible to change KVM's 'vcpu::regs[]' layout due to various reasons (e.g., emulation code uses decoded register index as array index to access the register). Therefore, adjust 'struct tdx_module_args' to match KVM's 'vcpu::regs[]' layout so that KVM can simply do below:
__seamcall_saved_ret(TDH_VP_ENTER, (struct tdx_module_args *)vcpu->arch.regs);
Note RAX/RSP/RBP are not used by the TDX_MODULE_CALL assembly, but they are necessary in order match the layout of 'struct tdx_module_args' to KVM's 'vcpu::regs[]'. Thus add them to the structure, but name them as *_unused. Also don't include them to asm-offset.c so that any misuse of them in the assembly would result in build error.
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sean Christopherson <seanjc@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Isaku Yamahata <isaku.yamahata@intel.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Kai Huang <kai.huang@intel.com> ---
v2 -> v3: - New patch
--- arch/x86/include/asm/shared/tdx.h | 19 +++++++++++++------ arch/x86/kernel/asm-offsets.c | 6 +++--- 2 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h index 74fc466dfdcd..8d1427562c63 100644 --- a/arch/x86/include/asm/shared/tdx.h +++ b/arch/x86/include/asm/shared/tdx.h @@ -58,24 +58,31 @@ * Used in __tdcall*() to gather the input/output registers' values of the * TDCALL instruction when requesting services from the TDX module. This is a * software only structure and not part of the TDX module/VMM ABI + * + * Note those *_unused are not used by the TDX_MODULE_CALL assembly. + * The layout of this structure also matches KVM's kvm_vcpu_arch::regs[] + * layout, which follows the "register index" order of x86 GPRs. KVM + * then can simply type cast kvm_vcpu_arch::regs[] to this structure to + * avoid the extra memory copy between two structures when making + * TDH.VP.ENTER SEAMCALL. */ struct tdx_module_args { - /* callee-clobbered */ + u64 rax_unused; u64 rcx; u64 rdx; + u64 rbx; + u64 rsp_unused; + u64 rbp_unused; + u64 rsi; + u64 rdi; u64 r8; u64 r9; - /* extra callee-clobbered */ u64 r10; u64 r11; - /* callee-saved + rdi/rsi */ u64 r12; u64 r13; u64 r14; u64 r15; - u64 rbx; - u64 rdi; - u64 rsi; }; /* Used to communicate with the TDX module */ diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c index 6913b372ccf7..e4ad822d3acd 100644 --- a/arch/x86/kernel/asm-offsets.c +++ b/arch/x86/kernel/asm-offsets.c @@ -70,6 +70,9 @@ static void __used common(void) BLANK(); OFFSET(TDX_MODULE_rcx, tdx_module_args, rcx); OFFSET(TDX_MODULE_rdx, tdx_module_args, rdx); + OFFSET(TDX_MODULE_rbx, tdx_module_args, rbx); + OFFSET(TDX_MODULE_rsi, tdx_module_args, rsi); + OFFSET(TDX_MODULE_rdi, tdx_module_args, rdi); OFFSET(TDX_MODULE_r8, tdx_module_args, r8); OFFSET(TDX_MODULE_r9, tdx_module_args, r9); OFFSET(TDX_MODULE_r10, tdx_module_args, r10); @@ -78,9 +81,6 @@ static void __used common(void) OFFSET(TDX_MODULE_r13, tdx_module_args, r13); OFFSET(TDX_MODULE_r14, tdx_module_args, r14); OFFSET(TDX_MODULE_r15, tdx_module_args, r15); - OFFSET(TDX_MODULE_rbx, tdx_module_args, rbx); - OFFSET(TDX_MODULE_rdi, tdx_module_args, rdi); - OFFSET(TDX_MODULE_rsi, tdx_module_args, rsi); BLANK(); OFFSET(BP_scratch, boot_params, scratch); -- 2.41.0
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