linux-kernel - Re: [PATCHv5 4/4] x86/tdx: Enable CPU topology enumeration

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Date: Wed, 3 Jul 2024 00:17:04 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Dave Hansen <dave.hansen@...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: linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv5 4/4] x86/tdx: Enable CPU topology enumeration

On 6/24/2024 7:41 PM, Kirill A. Shutemov wrote:
> TDX 1.0 defines baseline behaviour of TDX guest platform. In TDX 1.0
> generates a #VE when accessing topology-related CPUID leafs (0xB and
> 0x1F) and the X2APIC_APICID MSR. The kernel returns all zeros on CPUID
> topology. In practice, this means that the kernel can only boot with a
> plain topology. Any complications will cause problems.
> 
> The ENUM_TOPOLOGY feature allows the VMM to provide topology
> information to the guest. Enabling the feature eliminates
> topology-related #VEs: the TDX module virtualizes accesses to
> the CPUID leafs and the MSR.
> 
> Enable ENUM_TOPOLOGY if it is available.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>   arch/x86/coco/tdx/tdx.c           | 27 +++++++++++++++++++++++++++
>   arch/x86/include/asm/shared/tdx.h |  2 ++
>   2 files changed, 29 insertions(+)
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index ba3103877b21..f6e48119d6fd 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -249,6 +249,32 @@ static void disable_sept_ve(u64 td_attr)
>   	return;
>   }
>   
> +/*
> + * TDX 1.0 generates a #VE when accessing topology-related CPUID leafs (0xB and
> + * 0x1F) and the X2APIC_APICID MSR. The kernel returns all zeros on CPUID #VEs.
> + * In practice, this means that the kernel can only boot with a plain topology.
> + * Any complications will cause problems.
> + *
> + * The ENUM_TOPOLOGY feature allows the VMM to provide topology information.
> + * Enabling the feature  eliminates topology-related #VEs: the TDX module
> + * virtualizes accesses to the CPUID leafs and the MSR.
> + *
> + * Enable ENUM_TOPOLOGY if it is available.
> + */
> +static void enable_cpu_topology_enumeration(void)
> +{
> +	u64 configured;
> +
> +	/* Has the VMM provided a valid topology configuration? */
> +	tdg_vm_rd(TDCS_TOPOLOGY_ENUM_CONFIGURED, &configured);
> +	if (!configured) {
> +		pr_err("VMM did not configure X2APIC_IDs properly\n");
> +		return;
> +	}
> +
> +	tdg_vm_wr(TDCS_TD_CTLS, TD_CTLS_ENUM_TOPOLOGY, TD_CTLS_ENUM_TOPOLOGY);
> +}
> +
>   static void tdx_setup(u64 *cc_mask)
>   {
>   	struct tdx_module_args args = {};
> @@ -280,6 +306,7 @@ static void tdx_setup(u64 *cc_mask)
>   	tdg_vm_wr(TDCS_NOTIFY_ENABLES, 0, -1ULL);
>   
>   	disable_sept_ve(td_attr);
> +	enable_cpu_topology_enumeration();
>   }
>   
>   /*
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index fecb2a6e864b..89f7fcade8ae 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -23,12 +23,14 @@
>   #define TDCS_CONFIG_FLAGS		0x1110000300000016
>   #define TDCS_TD_CTLS			0x1110000300000017
>   #define TDCS_NOTIFY_ENABLES		0x9100000000000010

The ID for TDCS_NOTIFY_ENABLES I read from TDX spec is

	0x9110000300000010
	
> +#define TDCS_TOPOLOGY_ENUM_CONFIGURED	0x9100000000000019

and
	0x9110000000000019

for TOPOLOGY_ENUM_CONFIGURED.

Both version of them can work actually. But I'm curious where did you 
get them? just an old version of spec?
	
>   /* TDCS_CONFIG_FLAGS bits */
>   #define TDCS_CONFIG_FLEXIBLE_PENDING_VE	BIT_ULL(1)
>   
>   /* TDCS_TD_CTLS bits */
>   #define TD_CTLS_PENDING_VE_DISABLE	BIT_ULL(0)
> +#define TD_CTLS_ENUM_TOPOLOGY		BIT_ULL(1)
>   
>   /* TDX hypercall Leaf IDs */
>   #define TDVMCALL_MAP_GPA		0x10001