linux-kernel - Re: [PATCH v2 6/8] KVM: TDX: Handle TDG.VP.VMCALL<ReportFatalError>

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Message-ID: <Z6vo5sRyXTbtYSev@google.com>
Date: Tue, 11 Feb 2025 16:18:46 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: pbonzini@...hat.com, kvm@...r.kernel.org, rick.p.edgecombe@...el.com, 
	kai.huang@...el.com, adrian.hunter@...el.com, reinette.chatre@...el.com, 
	xiaoyao.li@...el.com, tony.lindgren@...el.com, isaku.yamahata@...el.com, 
	yan.y.zhao@...el.com, chao.gao@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/8] KVM: TDX: Handle TDG.VP.VMCALL<ReportFatalError>

On Tue, Feb 11, 2025, Binbin Wu wrote:
> +static int tdx_report_fatal_error(struct kvm_vcpu *vcpu)
> +{
> +	struct vcpu_tdx *tdx = to_tdx(vcpu);
> +	u64 reg_mask = tdx->vp_enter_args.rcx;
> +	u64 *opt_regs;
> +
> +	/*
> +	 * Skip sanity checks and let userspace decide what to do if sanity
> +	 * checks fail.
> +	 */
> +	vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> +	vcpu->run->system_event.type = KVM_SYSTEM_EVENT_TDX_FATAL;
> +	/* Error codes. */
> +	vcpu->run->system_event.data[0] = tdx->vp_enter_args.r12;
> +	/* GPA of additional information page. */
> +	vcpu->run->system_event.data[1] = tdx->vp_enter_args.r13;
> +	/* Information passed via registers (up to 64 bytes). */
> +	opt_regs = &vcpu->run->system_event.data[2];
> +
> +#define COPY_REG(REG, MASK)						\
> +	do {								\
> +		if (reg_mask & MASK) {					\

Based on past experience with conditionally filling kvm_run fields, I think KVM
should copy all registers and let userspace sort out the reg_mask.  Unless the
guest passes an ASCII byte stream exactly as the GHCI suggests, the information
is quite useless because userspace doesn't have reg_mask and so can't know what's
in data[4], data[5], etc...  And I won't be the least bit surprised if guests
deviate from the GHCI.

> +			*opt_regs = tdx->vp_enter_args.REG;		\
> +			opt_regs++;					\
> +		}							\
> +	} while (0)
> +
> +	/* The order is defined in GHCI. */

Assuming I haven't missed something, to hell with the GCHI, just dump *all*
registers, sorted by their index (ascending).  Including RAX (TDCALL), RBP, and
RSP.