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Message-ID: <15a13c5d-df88-46cf-8d88-2c8b94ff41ff@intel.com>
Date: Fri, 15 Mar 2024 10:18:52 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>, isaku.yamahata@...el.com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
Sagi Shahar <sagis@...gle.com>, chen.bo@...el.com, hang.yuan@...el.com,
tina.zhang@...el.com
Subject: Re: [PATCH v19 034/130] KVM: TDX: Get system-wide info about TDX
module on initialization
On 3/15/2024 7:09 AM, Huang, Kai wrote:
>
>> +struct tdx_info {
>> + u64 features0;
>> + u64 attributes_fixed0;
>> + u64 attributes_fixed1;
>> + u64 xfam_fixed0;
>> + u64 xfam_fixed1;
>> +
>> + u16 num_cpuid_config;
>> + /* This must the last member. */
>> + DECLARE_FLEX_ARRAY(struct kvm_tdx_cpuid_config, cpuid_configs);
>> +};
>> +
>> +/* Info about the TDX module. */
>> +static struct tdx_info *tdx_info;
>> +
>> #define TDX_MD_MAP(_fid, _ptr) \
>> { .fid = MD_FIELD_ID_##_fid, \
>> .ptr = (_ptr), }
>> @@ -66,7 +81,7 @@ static size_t tdx_md_element_size(u64 fid)
>> }
>> }
>> -static int __used tdx_md_read(struct tdx_md_map *maps, int nr_maps)
>> +static int tdx_md_read(struct tdx_md_map *maps, int nr_maps)
>> {
>> struct tdx_md_map *m;
>> int ret, i;
>> @@ -84,9 +99,26 @@ static int __used tdx_md_read(struct tdx_md_map
>> *maps, int nr_maps)
>> return 0;
>> }
>> +#define TDX_INFO_MAP(_field_id, _member) \
>> + TD_SYSINFO_MAP(_field_id, struct tdx_info, _member)
>> +
>> static int __init tdx_module_setup(void)
>> {
>> + u16 num_cpuid_config;
>> int ret;
>> + u32 i;
>> +
>> + struct tdx_md_map mds[] = {
>> + TDX_MD_MAP(NUM_CPUID_CONFIG, &num_cpuid_config),
>> + };
>> +
>> + struct tdx_metadata_field_mapping fields[] = {
>> + TDX_INFO_MAP(FEATURES0, features0),
>> + TDX_INFO_MAP(ATTRS_FIXED0, attributes_fixed0),
>> + TDX_INFO_MAP(ATTRS_FIXED1, attributes_fixed1),
>> + TDX_INFO_MAP(XFAM_FIXED0, xfam_fixed0),
>> + TDX_INFO_MAP(XFAM_FIXED1, xfam_fixed1),
>> + };
>> ret = tdx_enable();
>> if (ret) {
>> @@ -94,7 +126,48 @@ static int __init tdx_module_setup(void)
>> return ret;
>> }
>> + ret = tdx_md_read(mds, ARRAY_SIZE(mds));
>> + if (ret)
>> + return ret;
>> +
>> + tdx_info = kzalloc(sizeof(*tdx_info) +
>> + sizeof(*tdx_info->cpuid_configs) * num_cpuid_config,
>> + GFP_KERNEL);
>> + if (!tdx_info)
>> + return -ENOMEM;
>> + tdx_info->num_cpuid_config = num_cpuid_config;
>> +
>> + ret = tdx_sys_metadata_read(fields, ARRAY_SIZE(fields), tdx_info);
>> + if (ret)
>> + goto error_out;
>> +
>> + for (i = 0; i < num_cpuid_config; i++) {
>> + struct kvm_tdx_cpuid_config *c = &tdx_info->cpuid_configs[i];
>> + u64 leaf, eax_ebx, ecx_edx;
>> + struct tdx_md_map cpuids[] = {
>> + TDX_MD_MAP(CPUID_CONFIG_LEAVES + i, &leaf),
>> + TDX_MD_MAP(CPUID_CONFIG_VALUES + i * 2, &eax_ebx),
>> + TDX_MD_MAP(CPUID_CONFIG_VALUES + i * 2 + 1, &ecx_edx),
>> + };
>> +
>> + ret = tdx_md_read(cpuids, ARRAY_SIZE(cpuids));
>> + if (ret)
>> + goto error_out;
>> +
>> + c->leaf = (u32)leaf;
>> + c->sub_leaf = leaf >> 32;
>> + c->eax = (u32)eax_ebx;
>> + c->ebx = eax_ebx >> 32;
>> + c->ecx = (u32)ecx_edx;
>> + c->edx = ecx_edx >> 32;
>
> OK I can see why you don't want to use ...
>
> struct tdx_metadata_field_mapping fields[] = {
> TDX_INFO_MAP(NUM_CPUID_CONFIG, num_cpuid_config),
> };
>
> ... to read num_cpuid_config first, because the memory to hold @tdx_info
> hasn't been allocated, because its size depends on the num_cpuid_config.
>
> And I confess it's because the tdx_sys_metadata_field_read() that got
> exposed in patch ("x86/virt/tdx: Export global metadata read
> infrastructure") only returns 'u64' for all metadata field, and you
> didn't want to use something like this:
>
> u64 num_cpuid_config;
>
> tdx_sys_metadata_field_read(..., &num_cpuid_config);
>
> ...
>
> tdx_info->num_cpuid_config = num_cpuid_config;
>
> Or you can explicitly cast:
>
> tdx_info->num_cpuid_config = (u16)num_cpuid_config;
>
> (I know people may don't like the assigning 'u64' to 'u16', but it seems
> nothing wrong to me, because the way done in (1) below effectively has
> the same result comparing to type case).
>
> But there are other (better) ways to do:
>
> 1) you can introduce a helper as suggested by Xiaoyao in [*]:
>
>
> int tdx_sys_metadata_read_single(u64 field_id,
> int bytes, void *buf)
> {
> return stbuf_read_sys_metadata_field(field_id, 0,
> bytes, buf);
> }
>
> And do:
>
> tdx_sys_metadata_read_single(NUM_CPUID_CONFIG,
> sizeof(num_cpuid_config), &num_cpuid_config);
>
> That's _much_ cleaner than the 'struct tdx_md_map', which only confuses
> people.
>
> But I don't think we need to do this as mentioned above -- we just do
> type cast.
type cast needs another tmp variable to hold the output of u64.
The reason I want to introduce tdx_sys_metadata_read_single() is to
provide a simple and unified interface for other codes to read one
metadata field, instead of letting the caller to use temporary u64
variable and handle the cast or memcpy itself.
> [*]
> https://lore.kernel.org/lkml/bd61e29d-5842-4136-b30f-929b00bdf6f9@intel.com/T/#m2512e378c83bc44d3ca653f96f25c3fc85eb0e8a
>
>
>
>
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