[PULL 5/5] i386/kvm: add a comment explaining why .feat_names are commented out for Hyper-V feature bits

From: Eduardo Habkost <ehabkost@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: Eduardo Habkost <ehabkost@redhat.com>,
	kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: [PULL 5/5] i386/kvm: add a comment explaining why .feat_names are commented out for Hyper-V feature bits
Date: Mon, 14 Jan 2019 12:34:32 -0200	[thread overview]
Message-ID: <20190114143432.4771-6-ehabkost@redhat.com> (raw)
In-Reply-To: <20190114143432.4771-1-ehabkost@redhat.com>

From: Vitaly Kuznetsov <vkuznets@redhat.com>

Hyper-V .feat_names are, unlike hardware features, commented out and it is
not obvious why we do that. Document the current status quo.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20181221141604.16935-1-vkuznets@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target/i386/cpu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 3ece83696e..2f5412592d 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -929,6 +929,13 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
          */
         .no_autoenable_flags = ~0U,
     },
+    /*
+     * .feat_names are commented out for Hyper-V enlightenments because we
+     * don't want to have two different ways for enabling them on QEMU command
+     * line. Some features (e.g. "hyperv_time", "hyperv_vapic", ...) require
+     * enabling several feature bits simultaneously, exposing these bits
+     * individually may just confuse guests.
+     */
     [FEAT_HYPERV_EAX] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
-- 
2.18.0.rc1.1.g3f1ff2140
