linux-kernel - Re: [PATCH v2 16/25] KVM: TDX: Get system-wide info about TDX module on initialization

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Message-ID: <fa3d75e8-c459-4b8e-b76a-e4209a23838c@linux.intel.com>
Date: Thu, 31 Oct 2024 17:22:05 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Tony Lindgren <tony.lindgren@...ux.intel.com>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, pbonzini@...hat.com,
 seanjc@...gle.com, yan.y.zhao@...el.com, isaku.yamahata@...il.com,
 kai.huang@...el.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 xiaoyao.li@...el.com, reinette.chatre@...el.com,
 Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH v2 16/25] KVM: TDX: Get system-wide info about TDX module
 on initialization




On 10/31/2024 5:18 PM, Tony Lindgren wrote:
> On Thu, Oct 31, 2024 at 05:09:17PM +0800, Binbin Wu wrote:
>>
>>
>> On 10/31/2024 3:00 AM, Rick Edgecombe wrote:
>> [...]
>>> +static u32 tdx_set_guest_phys_addr_bits(const u32 eax, int addr_bits)
>>> +{
>>> +	return (eax & ~GENMASK(23, 16)) | (addr_bits & 0xff) << 16;
>>> +}
>>> +
>>> +#define KVM_TDX_CPUID_NO_SUBLEAF	((__u32)-1)
>>> +
>>> +static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char idx)
>>> +{
>>> +	const struct tdx_sys_info_td_conf *td_conf = &tdx_sysinfo->td_conf;
>>> +
>>> +	entry->function = (u32)td_conf->cpuid_config_leaves[idx];
>>> +	entry->index = td_conf->cpuid_config_leaves[idx] >> 32;
>>> +	entry->eax = (u32)td_conf->cpuid_config_values[idx][0];
>>> +	entry->ebx = td_conf->cpuid_config_values[idx][0] >> 32;
>>> +	entry->ecx = (u32)td_conf->cpuid_config_values[idx][1];
>>> +	entry->edx = td_conf->cpuid_config_values[idx][1] >> 32;
>>> +
>>> +	if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF)
>>> +		entry->index = 0;
>>> +
>>> +	/* Work around missing support on old TDX modules */
>>> +	if (entry->function == 0x80000008)
>>> +		entry->eax = tdx_set_guest_phys_addr_bits(entry->eax, 0xff);
>> Is it necessary to set bit 16~23 to 0xff?
>> It seems that when userspace wants to retrieve the value, the GPAW will
>> be set in tdx_read_cpuid() anyway.
> Leaving it out currently produces:
>
> qemu-system-x86_64: KVM_TDX_INIT_VM failed: Invalid argument
Yes, I forgot that userspace would use the value as the mask to filter cpuid.


>
> Regards,
>
> Tony