From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55078) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bwC5N-0001HI-Ae for qemu-devel@nongnu.org; Mon, 17 Oct 2016 13:52:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bwC5M-0002x7-7W for qemu-devel@nongnu.org; Mon, 17 Oct 2016 13:52:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54732) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1bwC5M-0002wB-1q for qemu-devel@nongnu.org; Mon, 17 Oct 2016 13:52:28 -0400 From: Eduardo Habkost Date: Mon, 17 Oct 2016 15:51:38 -0200 Message-Id: <1476726698-14661-22-git-send-email-ehabkost@redhat.com> In-Reply-To: <1476726698-14661-1-git-send-email-ehabkost@redhat.com> References: <1476726698-14661-1-git-send-email-ehabkost@redhat.com> Subject: [Qemu-devel] [PULL 21/21] target-i386: Don't use cpu->migratable when filtering features List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Paolo Bonzini , Richard Henderson , qemu-devel@nongnu.org When explicitly enabling unmigratable flags using "-cpu host" (e.g. "-cpu host,+invtsc"), the requested feature won't be enabled because cpu->migratable is true by default. This is inconsistent with all other CPU models, which don't have the "migratable" option, making "+invtsc" work without the need for extra options. This happens because x86_cpu_filter_features() uses cpu->migratable as an argument for x86_cpu_get_supported_feature_word(). This is not useful because: 2) on "-cpu host" it only makes QEMU disable features that were explicitly enabled in the command-line; 1) on all the other CPU models, cpu->migratable is already false. The fix is to just use 'false' as an argument to x86_cpu_get_supported_feature_word() in x86_cpu_filter_features(). Note that: * This won't change anything for people using using "-cpu host" or "-cpu host,migratable=" (with no extra features) because the x86_cpu_get_supported_feature_word() call on the cpu->host_features check uses cpu->migratable as argument. * This won't change anything for any CPU model except "host" because they all have cpu->migratable == false (and only "host" has the "migratable" property that allows it to be changed). * This will only change things for people using "-cpu host,+", where is a non-migratable feature. The only existing named non-migratable feature is "invtsc". In other words, this change will only affect people using "-cpu host,+invtsc" (that will now get what they asked for: the invtsc flag will be enabled). All other use cases are unaffected. Reviewed-by: Eric Blake Signed-off-by: Eduardo Habkost --- target-i386/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/target-i386/cpu.c b/target-i386/cpu.c index 754e575..d95514c 100644 --- a/target-i386/cpu.c +++ b/target-i386/cpu.c @@ -2248,7 +2248,7 @@ static int x86_cpu_filter_features(X86CPU *cpu) for (w = 0; w < FEATURE_WORDS; w++) { uint32_t host_feat = - x86_cpu_get_supported_feature_word(w, cpu->migratable); + x86_cpu_get_supported_feature_word(w, false); uint32_t requested_features = env->features[w]; env->features[w] &= host_feat; cpu->filtered_features[w] = requested_features & ~env->features[w]; -- 2.7.4