Messages in this thread | | | Date | Wed, 2 Aug 2023 14:39:30 -0700 | From | Isaku Yamahata <> | Subject | Re: [PATCH v3 12/12] x86/virt/tdx: Adjust 'struct tdx_module_args' to use x86 "register index" layout |
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On Wed, Jul 26, 2023 at 11:25:14PM +1200, Kai Huang <kai.huang@intel.com> wrote:
> 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.
Maybe we can have static check if the offsets match. e.g. BUILD_BUG_ON(__VCPU_REGS_RAX * 8 != TDX_MODULE_rax); etc...
Anyway, I can have such a patch in TDX KVM side when I use this function for TDH.VP.ENTER.
Thansk,
> > 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 >
-- Isaku Yamahata <isaku.yamahata@gmail.com>
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