From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226GQU4LnnSppMwxPaYcNLuCtI5jFhZOaTm4vedFgiThojuNzId6g29SFxxWjOxCFK+w4fj/ ARC-Seal: i=1; a=rsa-sha256; t=1517434987; cv=none; d=google.com; s=arc-20160816; b=rRH0xBCMIKaOafA5rOwrGXhOQfZZ/JA+AhPSa+MhjrN+piOAg6adQdfi9Vfv7QZy+2 fFeDzVSXE3lZxY2EF7LO7htN+yXuCBX5evWvI877EOUlP73vh1PrUfKRDTx6VcVPhOZj ITOwJqrQOCvRkCQkh765mdz0cvy7N2TfN/uFpYPwmNgelthLAUMvAvwa4YVq6wLlAJ69 35pouHUUXlM/h3bAPYT6PbEcIrKi9SL5TlyoXfvtNWAUt1ziHELVWTuBne297cIZVWsN zFLGdAKdTS412MtXiZsvADo/ihvfAzH8vg7HfRvhUSmOltTthCs4XqTK9HhSqcOU5Vg1 sMoA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :arc-authentication-results; bh=TVSzdzgByEYdxgGrlte/yejXxysqu43a/L1TeEdC0KY=; b=JeVdCbLqc/hSWD9ggEtKgdWoOhqY64sCr1xvGsNtIRfUr3AwTYywmAPejDv+HDeYM+ /12GAc1/BLU0CQihogr2f+RLfQBWOn+7uYnzzJcOUIgucMbzYuLcPHJTnum6sUdFn9Ri e+3kJ9+gfMcIwTZxShQqWgXsmTt8wVzRc5w9a0NHcVWobp1T5+ZJAlbn2FmvZXhcIdsA VRt+p2ZlVWgKQyjoXqsNZAfJfg+eSsGE1fU6kEvSjRy9r9rippJq0n5U1jqUnVyJtStE HMrIfwXAOEklyx+hIQ9f/tIHxZZWw724ulcIPci7IKvxTrRkvsDo21EQ8rKAqs9LhFE5 jG8g== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of pbonzini@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=pbonzini@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of pbonzini@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=pbonzini@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Subject: Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL To: Jim Mattson Cc: KarimAllah Ahmed , KarimAllah Ahmed , kvm list , LKML , the arch/x86 maintainers , Asit Mallick , Arjan Van De Ven , Dave Hansen , Andi Kleen , Andrea Arcangeli , Linus Torvalds , Tim Chen , Thomas Gleixner , Dan Williams , Jun Nakajima , David Woodhouse , Greg KH , Andy Lutomirski , Ashok Raj References: <1517427467-28567-1-git-send-email-karahmed@amazon.de> <1517427467-28567-5-git-send-email-karahmed@amazon.de> <06cb88da-f355-41ed-380f-7daa8ddf6159@amazon.com> <67dca2bb-1298-c7fa-f681-018e4edc6725@redhat.com> <16d89e09-fbfc-4a08-00a6-40cfb4776018@redhat.com> From: Paolo Bonzini Message-ID: Date: Wed, 31 Jan 2018 16:42:58 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1591113692084885209?= X-GMAIL-MSGID: =?utf-8?q?1591145909712071879?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 31/01/2018 16:05, Jim Mattson wrote: > On Wed, Jan 31, 2018 at 1:00 PM, Paolo Bonzini wrote: > >> Yes, but how would moving the field into struct loaded_vmcs do anything? >> Only vmon/vmoff would change anything in vmx->nested.vmcs02. > > My suggestion was that nested_vmx_merge_msr_bitmap should set the > vmcs02 version of save_spec_ctrl_on_exit based on the calculated value > of the write permission bit for IA32_SPEC_CTRL in the vmcs02 MSR > permission bitmap. > >> Even then, L1 vmexits will also be penalized because L1 has probably >> done an RDMSR/WRMSR on L2->L1 vmexit. So I don't think it's an issue? > > Yes, it sucks to be L1 in this situation. Can we just say it sucks to be L2 too? :) Because in the end as long as no one ever writes to spec_ctrl, everybody is happy. Paolo