Messages in this thread Patch in this message | | | From | "Huang, Kai" <> | Subject | Re: [PATCH v2 00/11] Unify TDCALL/SEAMCALL and TDVMCALL assembly | Date | Fri, 21 Jul 2023 11:02:50 +0000 |
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On Fri, 2023-07-21 at 10:06 +0200, Peter Zijlstra wrote: > On Fri, Jul 21, 2023 at 12:18:23AM +0000, Huang, Kai wrote: > > > Unfortunately I don't think it's feasible. Sean pointed out that > > kvm_vcpu_arch::regs[] do follow the "register index" hardware layout in x86 (for > > which I missed sorry), so we cannot re-order KVM part. > > > > And unfortunately RBP (5) is in middle of those registers: > > > > 0 = RAX > > 1 = RCX > > 2 = RDX > > 3 = RBX > > 4 = RSP > > 5 = RBP > > 6 = RSI > > 7 = RDI > > 8–15 represent R8–R15, respectively... > > > > Thus unless we add RBP to 'struct tdx_module_args', it's impossible to re-order > > the structure to match KVM's layout. > > Adding RBP to the struct shouldn't be a problem, we'll just not use it. > Same as RSP, nobody sane would expect that to be used. If you worry > about it you can give them funny names like: > > struct tdx_module_args { > unsigned long ax; > unsigned long cx; > unsigned long dx; > unsigned long bx; > unsigned long __sp_unused; > unsigned long __bp_unused; > unsigned long si; > unsigned long di; > ... > }; > > I mean, at this point the whole thing is just 128 bytes of data anyway.
Sure I can do.
How about adding an additional patch on top of this series?
For instance, below patch (compile only):
From c63d01bf91fe23f1e2d2e085644326bdee114d49 Mon Sep 17 00:00:00 2001 From: Kai Huang <kai.huang@intel.com> Date: Fri, 21 Jul 2023 22:06:31 +1200 Subject: [PATCH] x86/tdx: Add __seamcall_saved_ret() for TDH.VP.ENTER
For TDX guest, KVM uses TDH.VP.ENTER SEAMCALL leaf to enter the guest. When TDH.VP.ENTER returns to KVM due to TDG.VP.VMCALL from the TDX guest, all RCX/RDX/RBX/RDI/RSI/R8-R15 are valid output registers, and the following TDH.VP.ENTER also uses all those registers as input.
Introduce __seamcall_saved_ret(), which uses all above registers as both input/output, for KVM to support TDH.VP.ENTER.
Also, KVM caches guest's GPRs in 'kvm_vcpu_arch::regs[]', which follows follows the "register index" hardware layout of x86 GPRs. However the __seamcall_saved_ret() takes the pointer of 'struct tdx_module_args' as argument, thus there's a mismatch here.
One option is KVM to copy input registers from 'vcpu::regs[]' to a 'struct tdx_module_args' on the stack and use that 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[]' 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.
Signed-off-by: Kai Huang <kai.huang@intel.com> --- arch/x86/include/asm/shared/tdx.h | 19 +++++++++++++------ arch/x86/virt/vmx/tdx/seamcall.S | 19 +++++++++++++++++++ 2 files changed, 32 insertions(+), 6 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/virt/vmx/tdx/seamcall.S b/arch/x86/virt/vmx/tdx/seamcall.S index b32934837f16..f251ebadb014 100644 --- a/arch/x86/virt/vmx/tdx/seamcall.S +++ b/arch/x86/virt/vmx/tdx/seamcall.S @@ -40,3 +40,22 @@ SYM_FUNC_END(__seamcall) SYM_FUNC_START(__seamcall_ret) TDX_MODULE_CALL host=1 ret=1 SYM_FUNC_END(__seamcall_ret) + +/* + * __seamcall_saved_ret() - Host-side interface functions to SEAM software + * (the P-SEAMLDR or the TDX module), with saving output registers to the + * 'struct tdx_module_args' used as input. + * + * __seamcall_saved_ret() function ABI: + * + * @fn (RDI) - SEAMCALL Leaf number, moved to RAX + * @args (RSI) - struct tdx_module_args for input and output + * + * All registers in @args are used as input/output registers. + * + * Return (via RAX) TDX_SEAMCALL_VMFAILINVALID if the SEAMCALL itself + * fails, or the completion status of the SEAMCALL leaf function. + */ +SYM_FUNC_START(__seamcall_ret) + TDX_MODULE_CALL host=1 ret=1 saved=1 +SYM_FUNC_END(__seamcall_ret) -- 2.41.0
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