On 10/31/2024 5:09 PM, 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.
here it is to initialize the configurable CPUID bits that get reported
to userspace. Though TDX module doesn't allow them to be set in TD_PARAM
for KVM_TDX_INIT_VM, they get set to 0xff because KVM reuse these bits
EBX[23:16] as the interface for userspace to configure GPAW of TD guest
(implemented in setup_tdparams_eptp_controls() in patch 19). That's why
they need to be set as all-1 to allow userspace to configure.
And the comment above it is wrong and vague. we need to change it to
something like
/*
* Though TDX module doesn't allow the configuration of guest
* phys addr bits (EBX[23:16]), KVM uses it as the interface for
* userspace to configure the GPAW. So need to report these bits
* as configurable to userspace.
*/
+}
+
[...]
