linux-kernel - Re: [PATCH v8 09/11] x86/tdx: Add MSR support for TDX guest

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Date:   Wed, 6 Oct 2021 12:49:10 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 09/11] x86/tdx: Add MSR support for TDX guest

On Mon, Oct 04, 2021 at 07:52:03PM -0700, Kuppuswamy Sathyanarayanan wrote:
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index 3d0416515506..062ac4720434 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -110,6 +110,41 @@ static __cpuidle void tdx_safe_halt(void)
>  	_tdx_halt(irq_disabled, do_sti);
>  }
>  
> +static u64 tdx_read_msr_safe(unsigned int msr, int *err)

Here the kernel convention would probably be to return the error and
make 'val' an argument:

static int tdx_read_msr_safe(unsigned int msr, u64 *val)


> +{
> +	struct tdx_hypercall_output out = {0};
> +	u64 ret;
> +
> +	/*
> +	 * Emulate the MSR read via hypercall. More info about ABI
> +	 * can be found in TDX Guest-Host-Communication Interface
> +	 * (GHCI), sec titled "TDG.VP.VMCALL<Instruction.RDMSR>".
> +	 */
> +	ret = _tdx_hypercall(EXIT_REASON_MSR_READ, msr, 0, 0, 0, &out);
> +
> +	*err = ret ? -EIO : 0;
> +
> +	return out.r11;
> +}
> +
> +static int tdx_write_msr_safe(unsigned int msr, unsigned int low,
> +			      unsigned int high)
> +{
> +	u64 ret;
> +
> +	WARN_ON_ONCE(tdx_is_context_switched_msr(msr));

This fails to build, tdx_is_context_switched_msr() is missing.

> @@ -136,19 +171,33 @@ unsigned long tdx_get_ve_info(struct ve_info *ve)
>  int tdx_handle_virtualization_exception(struct pt_regs *regs,
>  					struct ve_info *ve)
>  {
> +	unsigned long val;
> +	int ret = 0;
> +
>  	switch (ve->exit_reason) {
>  	case EXIT_REASON_HLT:
>  		tdx_halt();
>  		break;
> +	case EXIT_REASON_MSR_READ:
> +		val = tdx_read_msr_safe(regs->cx, (unsigned int *)&ret);

Why the 'unsigned int *' cast?

Also, 'val' should have the same type as the one returned by
tdx_read_msr_safe().  (Though it technically doesn't matter here.)

-- 
Josh