linux-kernel - Re: [PATCH v6 05/10] x86/tdx: Handle port I/O

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Date:   Thu, 23 Sep 2021 11:32:27 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>
Cc:     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 v6 05/10] x86/tdx: Handle port I/O

On 9/22/21 5:52 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> TDX hypervisors cannot emulate instructions directly. This includes
> port IO which is normally emulated in the hypervisor. All port IO
> instructions inside TDX trigger the #VE exception in the guest and
> would be normally emulated there.
> 
> Also string I/O is not supported in TDX guest. So, unroll the string
> I/O operation into a loop operating on one element at a time. This
> method is similar to AMD SEV, so just extend the support for TDX guest
> platform.
> 
> Add a new confidential guest flag CC_ATTR_GUEST_UNROLL_STRING_IO to
> add string unroll support in asm/io.h
> 
> Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> ---
> 
> Changes since v5:
>   * Changed prot_guest_has() to cc_platform_has().
> 
> Changes since v4:
>   * Changed order of variable declaration in tdx_handle_io().
>   * Changed tdg_* prefix with tdx_*.
> 
> Changes since v3:
>   * Included PATTR_GUEST_UNROLL_STRING_IO protected guest flag
>     addition change in this patch.
>   * Rebased on top of Tom Lendacks protected guest change.
> 
> Changes since v2:
>   * None
> 
> Changes since v1:
>   * Fixed comments for tdg_handle_io().
>   * Used _tdx_hypercall() instead of __tdx_hypercall() in tdg_handle_io().
> 
>   arch/x86/include/asm/io.h   |  7 +++++--
>   arch/x86/kernel/cpu/intel.c |  1 +
>   arch/x86/kernel/tdx.c       | 35 +++++++++++++++++++++++++++++++++++
>   include/linux/cc_platform.h | 11 +++++++++++
>   4 files changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
> index fa6aa43e5dc3..67e0c4a0a0f4 100644
> --- a/arch/x86/include/asm/io.h
> +++ b/arch/x86/include/asm/io.h
> @@ -40,6 +40,7 @@
>   
>   #include <linux/string.h>
>   #include <linux/compiler.h>
> +#include <linux/cc_platform.h>
>   #include <asm/page.h>
>   #include <asm/tdx.h>
>   #include <asm/early_ioremap.h>
> @@ -310,7 +311,8 @@ static inline unsigned type in##bwl##_p(int port)			\
>   									\
>   static inline void outs##bwl(int port, const void *addr, unsigned long count) \
>   {									\
> -	if (sev_key_active()) {						\ > +	if (sev_key_active() ||						\
> +	    cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {		\

Would it make sense to make sev_key_active() and sev_enable_key generic 
and just re-use those instead of adding CC_ATTR_GUEST_UNROLL_STRING_IO and 
having multiple conditions here?

You can set the key in the TDX init routine just like SEV does.

Thanks,
Tom