RE: [PATCH v14 011/113] KVM: TDX: Add C wrapper functions for SEAMCALLs to the TDX module

[Wang, Wei W]

On Monday, May 29, 2023 12:19 PM, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> A VMM interacts with the TDX module using a new instruction (SEAMCALL).
> For instance, a TDX VMM does not have full access to the VM control
> structure corresponding to VMX VMCS.  Instead, a VMM induces the TDX
> module to act on behalf via SEAMCALLs.
> 
> Export __seamcall and define C wrapper functions for SEAMCALLs for
> readability.
> 
> Some SEAMCALL APIs donate host pages to TDX module or guest TD, and the
> donated pages are encrypted.  Such SEAMCALLs flush cache lines (typically by
> movdir64b instruction), but some don't.  Those that don't clear cache lines
> require the VMM to flush the cache lines to avoid cache line alias.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  arch/x86/include/asm/tdx.h       |   4 +
>  arch/x86/kvm/vmx/tdx_ops.h       | 202
> +++++++++++++++++++++++++++++++
>  arch/x86/virt/vmx/tdx/seamcall.S |   2 +
>  arch/x86/virt/vmx/tdx/tdx.h      |   3 -
>  4 files changed, 208 insertions(+), 3 deletions(-)  create mode 100644
> arch/x86/kvm/vmx/tdx_ops.h
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index
> 112a5b9bd5cd..6c01ab572c1f 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -104,10 +104,14 @@ static inline long tdx_kvm_hypercall(unsigned int
> nr, unsigned long p1,  bool platform_tdx_enabled(void);  int
> tdx_cpu_enable(void);  int tdx_enable(void);
> +u64 __seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
> +	       struct tdx_module_output *out);
>  #else	/* !CONFIG_INTEL_TDX_HOST */
>  static inline bool platform_tdx_enabled(void) { return false; }  static inline int
> tdx_cpu_enable(void) { return -EINVAL; }  static inline int tdx_enable(void)
> { return -EINVAL; }
> +static inline u64 __seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
> +			     struct tdx_module_output *out) { return
> TDX_SEAMCALL_UD; };
>  #endif	/* CONFIG_INTEL_TDX_HOST */
> 
>  #endif /* !__ASSEMBLY__ */
> diff --git a/arch/x86/kvm/vmx/tdx_ops.h b/arch/x86/kvm/vmx/tdx_ops.h
> new file mode 100644 index 000000000000..893cc6c25f3b
> --- /dev/null
> +++ b/arch/x86/kvm/vmx/tdx_ops.h
> @@ -0,0 +1,202 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* constants/data definitions for TDX SEAMCALLs */
> +
> +#ifndef __KVM_X86_TDX_OPS_H
> +#define __KVM_X86_TDX_OPS_H
> +
> +#include <linux/compiler.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/asm.h>
> +#include <asm/kvm_host.h>
> +
> +#include "tdx_errno.h"
> +#include "tdx_arch.h"
> +#include "x86.h"
> +
> +static inline u64 kvm_seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
> +			       struct tdx_module_output *out) {
> +	u64 ret;
> +
> +	ret = __seamcall(op, rcx, rdx, r8, r9, out);
> +	if (unlikely(ret == TDX_SEAMCALL_UD)) {
> +		/*
> +		 * TDX requires VMXON or #UD.  In the case of reboot or
> kexec,
> +		 * VMX is made off (VMXOFF) by kvm reboot notifier,
> +		 * kvm_reboot(), while TDs are still running.  The callers
> check
> +		 * the returned error and complain.  Suppress it by returning 0.
> +		 */

Curious how do the callers check the returned error when " Suppress
it by returning 0" here.


> +		kvm_spurious_fault();
> +		return 0;
> +	}
> +	return ret;
> +}