From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x2241RXDDEV/U3qoV+Uww24H4vRctgn1WiX+OB96AURg+eYGwOkkZLGGGaLrEf8s4mE1cwOpQ ARC-Seal: i=1; a=rsa-sha256; t=1517172001; cv=none; d=google.com; s=arc-20160816; b=cTo5aPlUwKR4arkTVVPuszkXvNyYCcz+nOO9pUisBor0TFNZH3bL+Te6b6Qswev/Mv UrchwS1mPjLqKlcoW3mIc5Uqwm1brpO+Pm0wZOVrXIswCykmXHgSQBAJYkb6rgjN1cKw X12l3UHXswo3sQ1A9qjo/MDAAYzloarmkUj1w0b4dq0SDGqmnrZ7G7Ixzkc7FWABwkPT 98KJif0yQTNC0PPri4bSyXuJNpgh6ozDsM4+amyQSb6jRoBBTqtw/V19G+snq+asj6hW PXUhkSEhLRD0lJIAlIZ7WMqyHNEQnYLBnKnD3DBODjnz5n4W8FrOKP4ScDeAGxNIgNFr ZBJA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:date:face:references:in-reply-to:cc:to:from:subject :message-id:dkim-signature:arc-authentication-results; bh=7I9KVRd0FDrXKaNoUcXJaL4QS8zc1krgFXvgTTwOnNE=; b=GjrmWFAlAvbY2X3VTQUrP1OpvNXKmHtrB5NJCzi9uqJ1Fmv2RHwgWzXJpiT4Hn27BH Ond3FlVKzMOCHFuq4++5epG90IlnfT0VfKi7rDbV+BH0YiSc2i8KedD8+67kGScaY0j9 ciS675UTmfJ4hT3QJNHhF/fu/Yo5KsjVD9OUP53j1a5R98eWFdGDQAhqQTWYYkYAFDZ5 wjnEkrIn19IR3LoCqYIajVo3BuxczdNt36Sze4dSoAdd8BPZmcJ+iWIrou0qlkfHLq4G lH60UZA5n9zsjR60h9/wXwLXIFRbtVwAQkpdHqWWPR0YNs1cLQB7XK4fGnczJrH7ZY5o 5DnA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=eYAGPtA+; spf=pass (google.com: best guess record for domain of batv+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=twosheds.20170209 header.b=eYAGPtA+; spf=pass (google.com: best guess record for domain of batv+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org designates 90.155.92.209 as permitted sender) smtp.mailfrom=BATV+bcac6755cd2ccc117aa4+5271+infradead.org+dwmw2@twosheds.srs.infradead.org Message-ID: <1517171968.6624.80.camel@infradead.org> Subject: Re: [PATCH] x86: vmx: Allow direct access to MSR_IA32_SPEC_CTRL From: David Woodhouse To: Konrad Rzeszutek Wilk , KarimAllah Ahmed , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Asit Mallick , Arjan Van De Ven , Dave Hansen , Andi Kleen , Andrea Arcangeli , Linus Torvalds , Tim Chen , Thomas Gleixner , Dan Williams , Jun Nakajima , Paolo Bonzini , Greg KH , Andy Lutomirski , Ashok Raj , daniel.kiper@oracle.com In-Reply-To: <4DCAF18F-C86A-4CBC-A9CC-CC01BF63313F@oracle.com> References: <1517167750-23485-1-git-send-email-karahmed@amazon.de> <4DCAF18F-C86A-4CBC-A9CC-CC01BF63313F@oracle.com> Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAG1BMVEUHBwcUFBQpKSlGRkZhYWF9fX2Xl5eysrLMzMxFF+rXAAACaElEQVQ4y21UQXbbIBQE9wJALmAg6ToWON22FrhZthHgbvssUPathC7QWMful2JHSmtWwGg+zPxBCE0DU4QoJQgRgsg4w2gJjBNE8PjFBZgnQMBs+uZ1NQNQjZO3BV4AGDFC0f+l4DBG0VUAM4yv7SO8IgRdHXQ+A78HKL5OAeCfNQV5cHX8DsBUyIJKtYbt98BKaGNCKjfgFVkqYVLbkHKsRsbSCSa0T6npIqLrpRBgQKHUpQmgs9eEKaiUcooE8WWfCGVnBiUcn1uF2XhbfmN9apKnmMP2K4kizKkQWxuaVNOpU2cACIyxO1Po8ETHcXEDMVnozcejkAYA9iaD4pU0ZvNQ8VurNnTuFAYVtuIPUZW25PjDIjQAlGyffIiRQxoWAZBmJ0LTdW2Nyc0iP3DqRhxizvGJkBWZmyFVyZkddWzmBoIBVMpCCJ1CFzl98xav4VJKSSD45KbUT75ixikTphDSRh8+Uz7JLgUTAgAFwzqzjxc/nDY7WUApqY0OMdTwCKZSXplSKkgIRCHElCp8ZnhnKqXuwcNbk1L0VXE+I9alUXoHlLHl3mv7/dWQlJwtjREC7mu9L/U2jQyMUuO2EDS4q9Kl2ddm232bxIE5pjJuVwiljNn/Cfv25/T0cu5cZbwHGVq7h/zp0B4n3S99V/utD+Uo8BiGx9xCsOAV5z7/tjo4Z4z1Lvb90KZ7eFOoOeXOukqF2seo234YYuaQPpRP+cVZU5adT1Edun5Iz3z8fTz3+eSDh0Ip1c7zx1MaijGzTd/3MbRuBHz8cvcVgCMBRpOHvgu59WDhoat+nIZm+LWm9C/aaaGq5DCP9QAAAABJRU5ErkJggg== Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-jgKKdAHNDSCmRhfKFBAc" Date: Sun, 28 Jan 2018 20:39:28 +0000 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590865729989295970?= X-GMAIL-MSGID: =?utf-8?q?1590870148085339622?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: --=-jgKKdAHNDSCmRhfKFBAc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2018-01-28 at 15:21 -0500, Konrad Rzeszutek Wilk wrote: > >To avoid the overhead of atomically saving and restoring the MSR_IA32_SP= EC_CTRL > >for guests that do not actually use the MSR, only add_atomic_switch_msr = when a > >non-zero is written to it. >=20 >=20 > We tried this and found that it was about 3% slower that doing the > old way of rdmsr and wrmsr. >=20 > But that was also with the host doing IBRS=C2=A0 as well. The common case will be that neither host nor guest are doing IBRS. Until the guest touches the MSR we do absolutely *nothing* with it, which is definitely the fastest option. --=-jgKKdAHNDSCmRhfKFBAc Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEFQw ggUxMIIEGaADAgECAhBNRhEyk/HZ7naOeTHWrzuAMA0GCSqGSIb3DQEBCwUAMIGXMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTAeFw0xNzEyMjEwMDAwMDBaFw0xODEyMjEyMzU5 NTlaMCQxIjAgBgkqhkiG9w0BCQEWE2R3bXcyQGluZnJhZGVhZC5vcmcwggEiMA0GCSqGSIb3DQEB AQUAA4IBDwAwggEKAoIBAQDgzLNWa18DNpGUj/ZeH0Sgz53ESIbzdPw3OJeuNP6jZhxZojbyfxbM hETscxI/Hj6UZ4a7sHm5BkVjlsB1Af2Za/PXUt8MmLAcPMHkMPGunvkUibEvblDvpqMkQZlaZM+t 5PqFmWkbehLaEvbpNY7dmEAAeKh4klTzJzrr5AAzaCQ32cA2e3+DEIv5O5l9ViMIjy/JM+xMQrfX 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