Re: [RFC PATCH v2 01/26] x86/cpufeatures: Add SGX1 and SGX2 sub-features

On Tue, 2021-01-19 at 10:03 -0800, Sean Christopherson wrote:

On Tue, Jan 19, 2021, Borislav Petkov wrote:

quoted

On Mon, Jan 18, 2021 at 04:26:49PM +1300, Kai Huang wrote:

quoted

diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index 3b1b01f2b248..7937a315f8cf 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c

@@ -96,7 +96,6 @@ static void init_vmx_capabilities(struct cpuinfo_x86 *c)

 static void clear_sgx_caps(void)
 {
 	setup_clear_cpu_cap(X86_FEATURE_SGX);
-	setup_clear_cpu_cap(X86_FEATURE_SGX_LC);

Why is that line being removed here?

Shouldn't this add SGX1 and SGX2 here instead as this function is
supposed to, well, *clear* sgx caps on feat_ctl setup failures or
"nosgx" cmdline?

Doesn't adding making the SGX sub-features depend on X86_FEATURE_SGX have the
same net effect?  Or am I misreading do_clear_cpu_cap()?

On my testing machine with SGX, SGX_LC, and SGX1. I just double tested that clearing
X86_FEATURE_SGX also clears SGX1 and SGX_LC bits.

Though if we use the cpuid_deps table, I'd vote to get rid of clear_sgx_caps()
and call setup_clear_cpu_cap(X86_FEATURE_SGX) directly. 

Yes I can do that.

 And probably change the
existing SGX_LC behavior and drop clear_sgx_caps() in a separate patch instead
of squeezing it into this one.

To double confirm, you want:

1) This patch to introduce SGX1, SGX2, and also put SGX1 and SGX2 in to CPUID
dependency table; 
2) A separate patch to put SGX_LC to CPUID dependency table too, and also git rid of
clear_sgx_caps()

Correct?

Btw, in your original patch, both SGX1 and SGX2 depends on SGX, but I changed to make
SGX2 depend on SGX1. However I still make SGX_LC depend on SGX, but not SGX1. Does
this make sense to you?