linux-kernel - PKEY syscall number for selftest? (was: [PATCH 4/7] KVM: TDX: restore host xsave state when exit from the guest TD)

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Message-ID: <Z2Xgo3XwE6XrCMOM@google.com>
Date: Fri, 20 Dec 2024 13:24:51 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: PKEY syscall number for selftest? (was: [PATCH 4/7] KVM: TDX: restore
 host xsave state when exit from the guest TD)

Switching topics, dropped everyone else except the list.

On Fri, Dec 20, 2024, Sean Christopherson wrote:
>  arch/x86/kvm/x86.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4320647bd78a..9d5cece9260b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1186,7 +1186,7 @@ void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
>  	    vcpu->arch.pkru != vcpu->arch.host_pkru &&
>  	    ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
>  	     kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE)))
> -		write_pkru(vcpu->arch.pkru);
> +		wrpkru(vcpu->arch.pkru);
>  }
>  EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
>  
> @@ -1200,7 +1200,7 @@ void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
>  	     kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
>  		vcpu->arch.pkru = rdpkru();
>  		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> -			write_pkru(vcpu->arch.host_pkru);
> +			wrpkru(vcpu->arch.host_pkru);
>  	}
>  
>  	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
> 
> base-commit: 13e98294d7cec978e31138d16824f50556a62d17
> -- 

I tried to test this by running the mm/protection_keys selftest in a VM, but it
gives what are effectively false passes on x86-64 due to the selftest picking up
the generic syscall numbers, e.g. 289 for SYS_pkey_alloc, instead of the x86-64
numbers.

I was able to get the test to run by hacking tools/testing/selftests/mm/pkey-x86.h
to shove in the right numbers, but I can't imagine that's the intended behavior.

If I omit the #undefs from pkey-x86.h, it shows that the test is grabbing the
definitions from the generic usr/include/asm-generic/unistd.h header.

Am I doing something stupid?

Regardless of whether this is PEBKAC or working as intended, on x86, the test
should ideally assert that "ospke" support in /proc/cpuinfo is consistent with
the result of sys_pkey_alloc(), e.g. so that an failure to allocate a pkey on a
system that work is reported as an error, not a pass.

--
diff --git a/tools/testing/selftests/mm/pkey-x86.h b/tools/testing/selftests/mm/pkey-x86.h
index ac91777c8917..ccc3552e6b77 100644
--- a/tools/testing/selftests/mm/pkey-x86.h
+++ b/tools/testing/selftests/mm/pkey-x86.h
@@ -3,6 +3,10 @@
 #ifndef _PKEYS_X86_H
 #define _PKEYS_X86_H
 
+#define __NR_pkey_mprotect     329
+#define __NR_pkey_alloc                330
+#define __NR_pkey_free         331
+
 #ifdef __i386__
 
 #define REG_IP_IDX             REG_EIP
--

Yields:

$ ARCH=x86_64 make protection_keys_64
gcc -Wall -I /home/sean/go/src/kernel.org/linux/tools/testing/selftests/../../..  -isystem /home/sean/go/src/kernel.org/linux/tools/testing/selftests/../../../usr/include -isystem /home/sean/go/src/kernel.org/linux/tools/testing/selftests/../../../tools/include/uapi -no-pie -D_GNU_SOURCE=  -m64 -mxsave  protection_keys.c vm_util.c thp_settings.c -lrt -lpthread -lm -lrt -ldl -o /home/sean/go/src/kernel.org/linux/tools/testing/selftests/mm/protection_keys_64
In file included from pkey-helpers.h:102:0,
                 from protection_keys.c:49:
pkey-x86.h:6:0: warning: "__NR_pkey_mprotect" redefined
 #define __NR_pkey_mprotect 329
 
In file included from protection_keys.c:45:0:
/home/sean/go/src/kernel.org/linux/usr/include/asm-generic/unistd.h:693:0: note: this is the location of the previous definition
 #define __NR_pkey_mprotect 288
 
In file included from pkey-helpers.h:102:0,
                 from protection_keys.c:49:
pkey-x86.h:7:0: warning: "__NR_pkey_alloc" redefined
 #define __NR_pkey_alloc  330
 
In file included from protection_keys.c:45:0:
/home/sean/go/src/kernel.org/linux/usr/include/asm-generic/unistd.h:695:0: note: this is the location of the previous definition
 #define __NR_pkey_alloc 289
 
In file included from pkey-helpers.h:102:0,
                 from protection_keys.c:49:
pkey-x86.h:8:0: warning: "__NR_pkey_free" redefined
 #define __NR_pkey_free  331
 
In file included from protection_keys.c:45:0:
/home/sean/go/src/kernel.org/linux/usr/include/asm-generic/unistd.h:697:0: note: this is the location of the previous definition
 #define __NR_pkey_free 290