Message-ID: <c99d0b82-a44f-db8e-3f81-93d2394f9a02@redhat.com>
Date:   Wed, 5 Jan 2022 14:06:40 +0100
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Subject: Re: [PATCH v5 07/21] x86/fpu: Provide fpu_enable_guest_xfd_features()
 for KVM
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To:     Yang Zhong <yang.zhong@intel.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, corbet@lwn.net, shuah@kernel.org,
        seanjc@google.com
Cc:     jun.nakajima@intel.com, kevin.tian@intel.com,
        jing2.liu@linux.intel.com, jing2.liu@intel.com,
        guang.zeng@intel.com, wei.w.wang@intel.com
References: <20220105123532.12586-1-yang.zhong@intel.com>
 <20220105123532.12586-8-yang.zhong@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <20220105123532.12586-8-yang.zhong@intel.com>
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On 1/5/22 13:35, Yang Zhong wrote:
> +int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures)
> +{
> +	lockdep_assert_preemption_enabled();
> +

The old fpu_update_guest_perm_features(guest_fpu) is equivalent to

	fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);

Missing doc comment:

/*
  * fpu_enable_guest_xfd_features - Enable xfeatures according to guest perm
  * @guest_fpu:         Pointer to the guest FPU container
  * @xfeatures:         Features requested by guest CPUID
  *
  * Enable all dynamic xfeatures according to guest perm and requested CPUID.
  * Invoked if the caller wants to conservatively expand fpstate buffer instead
  * of waiting until XCR0 or XFD MSR is written.
  *
  * Return: 0 on success, error code otherwise
  */

Also, the check for 32-bit is slightly imprecise:

	/* Dynamic xfeatures are not supported with 32-bit kernels. */
	if (!IS_ENABLED(CONFIG_X86_64))
-		return 0;
+		return -EINVAL;

since we only get here with xfeatures != 0 (if it compiles, just removing
the IS_ENABLED check altogether would be even better).  With these changes,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo