linux-kernel - Re: [PATCHv2 13/29] x86/tdx: Add port I/O emulation

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Message-ID: <YfojFe6Rh0ETLc28@zn.tnic>
Date:   Wed, 2 Feb 2022 07:22:13 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 13/29] x86/tdx: Add port I/O emulation

On Mon, Jan 24, 2022 at 06:01:59PM +0300, Kirill A. Shutemov wrote:
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index 8e630eeb765d..e73af22a4c11 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -13,6 +13,12 @@
>  /* TDX module Call Leaf IDs */
>  #define TDX_GET_VEINFO			3
>  
> +/* See Exit Qualification for I/O Instructions in VMX documentation */
> +#define VE_IS_IO_IN(exit_qual)		(((exit_qual) & 8) ? 1 : 0)
> +#define VE_GET_IO_SIZE(exit_qual)	(((exit_qual) & 7) + 1)
> +#define VE_GET_PORT_NUM(exit_qual)	((exit_qual) >> 16)
> +#define VE_IS_IO_STRING(exit_qual)	((exit_qual) & 16 ? 1 : 0)

Use BIT() and masks here. For example:

#define VE_IS_IO_STRING(e)	((e) & BIT(4))

You don't need the ternary ?: either as you're using them all in a
boolean context.

> +static bool tdx_handle_io(struct pt_regs *regs, u32 exit_qual)
> +{
> +	struct tdx_hypercall_output out;
> +	int size, port, ret;
> +	u64 mask;
> +	bool in;
> +
> +	if (VE_IS_IO_STRING(exit_qual))
> +		return false;
> +
> +	in   = VE_IS_IO_IN(exit_qual);
> +	size = VE_GET_IO_SIZE(exit_qual);
> +	port = VE_GET_PORT_NUM(exit_qual);
> +	mask = GENMASK(BITS_PER_BYTE * size, 0);
> +
> +	/*
> +	 * Emulate the I/O read/write via hypercall. More info about
> +	 * ABI can be found in TDX Guest-Host-Communication Interface
> +	 * (GHCI) sec titled "TDG.VP.VMCALL<Instruction.IO>".

"section"

> +	 */
> +	ret = _tdx_hypercall(EXIT_REASON_IO_INSTRUCTION, size, !in, port,
> +			     in ? 0 : regs->ax, &out);
> +	if (!in)
> +		return !ret;
> +
> +	regs->ax &= ~mask;
> +	regs->ax |= ret ? UINT_MAX : out.r11 & mask;
> +
> +	return !ret;
> +}

-- 
Regards/Gruss,
    Boris.

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