From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (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 37A1728C5C5 for ; Tue, 22 Apr 2025 14:40:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745332810; cv=none; b=MrvsF29AqGe5eL+1zW/qMcNgMmzrJU/fpraYn4TgYcbE9oa8usMhJK05s+B4p3yzZF+GyWmYPJ4ZBe07xLUhI1VoHU1mLV+i9oY1WVeBclr9nGEdiNYF+FBoOJb0e0bJxbLfpHYl5ZhAnMRW34IfNxZIiF9s3e4P9mlFMXbRb28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745332810; c=relaxed/simple; bh=H6SmG8zfZRpF/NNqVIU+UMtU8feZniQBwXGO2NIJxnI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=qAoQtKq+GcaiPuqEiNcH9ilTY79SETbltj0eLcF4gSMLoRtAc3vr8hQHnKFTVc3J/CZlyVG+YdYTdFMBFmUNZdVmFXgVgMCkUhSyXzwPCxCcvE7ewisngsvJpBNWATCVzaNNhxEYSjRJOLQ+BUkgbBLd+6I3P2DqEeKIoKlobl4= 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=xvXnzesv; arc=none smtp.client-ip=209.85.210.201 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="xvXnzesv" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-73c205898aaso3828245b3a.2 for ; Tue, 22 Apr 2025 07:40:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1745332808; x=1745937608; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=4kse3i/9a2wXrwb5fWBr/bq3/Gxj8YgN5EpIYvK3Crk=; b=xvXnzesvHWT/qlP1TLbvjkE4GSmpWLvuTlXNUaJC/YuXFkpIW8mmmsIrXTYdUJhYep Rvz1SJEJu+lJadVid+8bcN6eOiEooQhqRy3pWE3bdJsv/9ckXiToNza4vLVnVMlj8khC XSG0vBB97OASdnelxP4pwe/k3p33sXRzRsDuG/FglT9Hm7sWqdLtrJzVoUgWgOjjhx7N lUtu0HlhI1x6Nf3Ad1UPiEJ23HBI+mHlPpNl1MML6HXDH7gHShw+XOTN7pqrh/CthvQb 48gbAZnB0KfIUPjP3LNoyHDxa+CwIwMdlUzhv1pqDktGSqHqbVMJfs5zNWLL5pxg7o5X l5ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1745332808; x=1745937608; h=content-transfer-encoding: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=4kse3i/9a2wXrwb5fWBr/bq3/Gxj8YgN5EpIYvK3Crk=; b=FFczAD4AS3Di6x6VQC/843zkl2cKpN7+dr3FlkewY9ORgKQwLntQZ7wh1B8V0oSGG0 HLfah2lv4NHSbYPxpaBHBpQUMUlH+Ntrl/ONKXxzQVuim0biIq9vnrc84XtJ/GCNQvlY CAihNkKq3KuV9GOADnz0wz6mv2XSEwmZcs0rJleQFwA2usP3+qbnpFKXI4Rpd4EKXO7W IL/xwFmglEJbR1OXARWrUEYucGo41vm/XXHmfSxY/4kujLHD8dWcp5HhzQaxQKn1YbZc i42bQivK1tDrabMpZa5OJEHdki1nZyR+EYiWwsmLef//XNYZI76yPlJEKrzKbDxr8Wqy rk/A== X-Forwarded-Encrypted: i=1; AJvYcCXcjbtFNtJKghrKRPeFRp9ilmtUxMVvSyoc8O+8+40nATNnPhn5zjMaZLs1aTBV9g3q2Lo=@vger.kernel.org X-Gm-Message-State: AOJu0YxNwzo8hm0BKArFkJRQgXY2Vt6EjhY08/w2nJTt/QiHLiixebDW XJa7WvUrvi/f/aYx4K9kTEMEPgHKyI70O+kWtt6zqbVPCOpe4flCin6GfT4c3I6iou+DZiIoq4h Oew== X-Google-Smtp-Source: AGHT+IEqJub0IjABqAHfS37ByzLd7WwIavXyDFMuCxLJ5z8Czie0a5FeUJW/ZUjHDlbSCiXqb7H4nSjCbvU= X-Received: from pfbgq27.prod.google.com ([2002:a05:6a00:3bdb:b0:737:6b9f:8ab4]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a62:f24e:0:b0:73d:ff02:8d83 with SMTP id d2e1a72fcca58-73dff028da0mr4353385b3a.3.1745332808429; Tue, 22 Apr 2025 07:40:08 -0700 (PDT) Date: Tue, 22 Apr 2025 07:40:06 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: Message-ID: Subject: Re: MSR access API uses in KVM x86 From: Sean Christopherson To: Xin Li Cc: Paolo Bonzini , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "H. Peter Anvin" , Ingo Molnar Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Mon, Apr 21, 2025, Xin Li wrote: > It looks to me that MSR access API uses in KVM x86 are NOT consistent; > sometimes {wr,rd}msrl() are used and sometimes native_{wr,rd}msrl() are > used. >=20 > Was there a reason that how a generic or native MSR API was chosen? I doubt anyone knows for sure; that'd likely require a time travelling devi= ce and/or telepathic abilities :-) > In my opinion KVM should use the native MSR APIs, which can streamline > operations and potentially improve performance by avoiding the overhead > associated with generic MSR API indirect calls when CONFIG_XEN_PV=3Dy. As J=C3=BCrgen pointed out, they aren't indirect calls. Though IIUC, there= is still a direct CALL and thus a RET when PARAVIRT_XXL=3DY. I agree that using PV APIs in KVM doesn't make much sense, as running KVM i= n a XEN PV guest doesn't seem like something we should optimize for, if it's ev= en supported. So if we end up churning all of the rdmsr/wrmsr macros, I have = no objection to switching to native variants. Though if we do that, it would be nice if there's a way to avoid the "nativ= e_" prefix everywhere, for the sake of readability.