From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B5C8C20DC5 for ; Fri, 12 Jul 2024 19:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720812613; cv=none; b=rB6Lq/VzTJSJBcKTL52R5hJqU1N8Joggu4MD4AOZiDOpmoErRX9MuueoEHcvZuEXiSGa/kECLdhUXbwevGjuEBiQIdXtspYebZabrZMt6i1hqe8yijUB+2PG2JcpGMEwta6IsoHyJ6xq/RX/YgGLH4y/lCL6ioN8bRimVRSWzYM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720812613; c=relaxed/simple; bh=J1S9Co/gsUdc+1Ynd0QU/qO2abhM1ZoN3G8Rcdw3+Yc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=JTVWrY4DTeFWjjzJSxBaeN8f5zRnpjNfZSONf1grTvOppUqx4u5sTa9C+2LiUg/D0dHFJBjtg6Q9sPK/XsN7ZkDvgdoZg0aA6PjjJp9jLUFyBxOIt6lFCrhVFKlO/FwejSns9M2+5nf9w8eYIq4pt5wshNfRpLo2RqQ0LbIMzxs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=t485Ih32; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="t485Ih32" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-654d96c2bb5so39665737b3.2 for ; Fri, 12 Jul 2024 12:30:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1720812611; x=1721417411; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=jSam3OFYUTe13VOqHa17qoJuTdcVQF9rMQXxc9I3He4=; b=t485Ih32RA0LWmsHUxeRNy7ExFkrZDYEeaewkl/7DCdFuG6occGvzO4BVrWYtjsZE/ prV+To05bCR7pkosC+zYi5EVpB/SY/B4rU+ykZrokfihdgpveNdspklpO9ScWlGUkAbf oRs8k3cTBd8wUOBUAL8r9ejxnxwVQd9cdCqfI4LTLdkVRjSAejW2jszlduc2x2ipmSlv ItnNI7lgu/D+ihPSEdwzY0U6LDSLUhQIpIujgm2Xwt15WQWUMCXXlgnFo1T1hbpMhvRS TpDtnJ7Z7MAxZIYKGzPYyTEAlQXcxD5PT+K9iKluvN6pzoh0uPj93ncfR4seGkDdcmB6 jwGw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1720812611; x=1721417411; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=jSam3OFYUTe13VOqHa17qoJuTdcVQF9rMQXxc9I3He4=; b=frxVqtN0SF8Pmj12On1immc8TV9c/Png+zJUadTMXp4mcuxS6T+TM/L7RkOWE2Pa91 /UJ0K9Ke8n0w/ofNi4389WlF62KbzOKaMSzUs9mn0PnBFgnkAGDzwvAbhx6ZfAH8cO/i bKOmAgmG98llof4ym7kpEAHwWwlqwGrU+fXW8PtUhe5I4nyw3d9soVomOwK7Dobanloq 1GEtPwRMoFM0yYjOWM91ZCxiBBukbGvOEBkrWgMP6Jwm8/GALaDNk/JjSd0lhs20qlO4 qFWTzPplD+Z4wXGvHVWFOn+7qC3hh0hdvjjMMnTPnMYUgSmT1qku1Nt+csP/CBGBu2fS JJ/g== X-Forwarded-Encrypted: i=1; AJvYcCXqKpd1KAbZ+3zAgP0McGZp7E10euyjrnCbZFdZsckRMSo0YVGLcJgoJLizQ9N4s04RevrZrxN1XDeESdrFmf0owiL8zIcNXA3k X-Gm-Message-State: AOJu0YyybQ70CsbAVb/z7/QCF2EBRycxhwK+c9Y9UUVjmBss6sJAEA0V Uf0vKKPn38G+CoKcsXhaMAeXnkeUpIfLeKHYtApS7YLmarXabRG/gRQXgYCG4+3M4Q8YpkYzS/8 NoQ== X-Google-Smtp-Source: AGHT+IHDX6aq/IiCOt698IqpZ4MrQ2IJcf1EwlXXpiuV+/DiG8Es8j3Np/1XnI0oCcG1Eu1pGoFCApjvBVw= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:6381:b0:64b:7f7e:910f with SMTP id 00721157ae682-658f07d5705mr557917b3.7.1720812610774; Fri, 12 Jul 2024 12:30:10 -0700 (PDT) Date: Fri, 12 Jul 2024 12:30:09 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240207172646.3981-1-xin3.li@intel.com> <20240207172646.3981-10-xin3.li@intel.com> Message-ID: Subject: Re: [PATCH v2 09/25] KVM: VMX: Switch FRED RSP0 between host and guest From: Sean Christopherson To: Xin3 Li Cc: "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "pbonzini@redhat.com" , "corbet@lwn.net" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "shuah@kernel.org" , "vkuznets@redhat.com" , "peterz@infradead.org" , Ravi V Shankar , "xin@zytor.com" Content-Type: text/plain; charset="us-ascii" On Fri, Jul 12, 2024, Xin3 Li wrote: > > > > E.g. if it's somewhere in task_struct, then kvm_on_user_return() > > > > would restore the current task's desired RSP0. > > > > > > So you're suggesting to extend the framework to allow per task constants? > > > > Yeah, or more likely, special case MSR_IA32_FRED_RSP0. If KVM didn't already > > have the user return framework, I wouldn't suggest this as I doubt avoiding > > WRMSR when switching between vCPU tasks will be very meaningful, but it's > > easy to handle FRED_RSP0, so why not. > > Great, I will take the patch. > > It looks to me that this also works for KERNEL GS BASE MSR, no? I don't think so, because the kernel expects MSR_KERNEL_GS_BASE to be accurate when querying GS.base for the current task: unsigned long x86_gsbase_read_task(struct task_struct *task) { unsigned long gsbase; if (task == current) gsbase = x86_gsbase_read_cpu_inactive(); else if (boot_cpu_has(X86_FEATURE_FSGSBASE) || (task->thread.gsindex == 0)) gsbase = task->thread.gsbase; else gsbase = x86_fsgsbase_read_task(task, task->thread.gsindex); return gsbase; }