Received: by 2002:a05:6a10:8c0a:0:0:0:0 with SMTP id go10csp3940909pxb; Mon, 8 Feb 2021 04:11:18 -0800 (PST) X-Google-Smtp-Source: ABdhPJyIHes1B8PaZrwvLOky8NiTfjYlwtlTohwn7ub99Ditt4cR+F13lgtSwQequJjwpRHyqBUl X-Received: by 2002:a05:6402:4391:: with SMTP id o17mr17033604edc.196.1612786278135; Mon, 08 Feb 2021 04:11:18 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1612786278; cv=none; d=google.com; s=arc-20160816; b=o7wfZquuWjInbAKhAMPNzBC82O/EIPMi1yoNfnQqU7Fju/R8u93C/lf4QHimWBsVm4 /Rw27H/rELJdD1U02/GGimgXc3p/PFjt/cdtLtCv+dAhw7+wQ/0hld8lS8QCe681HuDk 30Si3cxvWDEgDUo3PBc4fAics2DaNAUREzPZkWPOKAiRTzUeulPIoQRvn/4PlxehhqrF IVdXcoxkwaWlDNF3La6+SBwIUJByTCMWB7H+xfpK42NWTeuZAgp8j3+Rqto1faJ1x3Qo /mmMMVNxvKyiBmQNGmKWqUUoBWvYqb2+evBhJw9uakVKGfQ9AGOHABk4iE9HjohIFyri qO9A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:in-reply-to:mime-version:user-agent:date :message-id:from:references:cc:to:subject:dkim-signature; bh=rNXEQttSljSOXQ5vUQs4GTPYC1r1hAnr6viwolFR9tc=; b=ILWQ5XGVwQIPkKHj4f/tjDK5mWG3eWkcvSr+PFBsM4IDsBbS6NbonPEMoGLRzmuSr2 gZJmgsT526k7kQrar+xy/vwa0u/YBXLwiZzIfirvOicLotPoAe6Kvebzozw3ekluwC+a sxQhe3UOW3YiFzjgHR3oscoVCGqM8yuksEqf8LK72K9OiEJfGBgONr1OmKd3BZyWIvMM UKvKK+vAkhLvFzLcjHe0WzzXoSaCgLFmGIVnslXGWKpOboWSHfsrkcmFqSVrqVT8HD+R 7k/xeHGtKmODSFOO8KEUYoBxTZLKlsgKRhiyiNVVgRn8yNkEFNVrsqPtcHsPgrTkZn99 B7KA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=r5dHf4kF; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=NONE dis=NONE) header.from=suse.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id i12si1715947edx.217.2021.02.08.04.10.53; Mon, 08 Feb 2021 04:11:18 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@suse.com header.s=susede1 header.b=r5dHf4kF; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=NONE dis=NONE) header.from=suse.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229980AbhBHMJT (ORCPT + 99 others); Mon, 8 Feb 2021 07:09:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:60666 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233386AbhBHLtj (ORCPT ); Mon, 8 Feb 2021 06:49:39 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1612784930; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rNXEQttSljSOXQ5vUQs4GTPYC1r1hAnr6viwolFR9tc=; b=r5dHf4kFkxHmbA04PtcbaZu0atntZZsdLD35oGLActq/Hd9uIGmlaQlRW9pfEuXFvBrHX5 pA45TfkeavAOujIRJ0MsmqAbaLd8GrbmDqnk4HxAft3rabux3DqyLXtnjfJuim2oOcFINC wag2fddgjXcY/urh6k3eta9Qg6GdWD0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E9F48AD4E; Mon, 8 Feb 2021 11:48:49 +0000 (UTC) Subject: Re: [PATCH 7/7] xen/evtchn: read producer index only once To: Julien Grall , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Stefano Stabellini References: <20210206104932.29064-1-jgross@suse.com> <20210206104932.29064-8-jgross@suse.com> <8032d8a9-b28f-95e1-a5a8-e955ada4dc0a@xen.org> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <969f1492-764b-3345-eb65-64aca554ce9e@suse.com> Date: Mon, 8 Feb 2021 12:48:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <8032d8a9-b28f-95e1-a5a8-e955ada4dc0a@xen.org> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="MibTRswBhznEAVzFPSZwv0FK78kpDjPYj" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --MibTRswBhznEAVzFPSZwv0FK78kpDjPYj Content-Type: multipart/mixed; boundary="EKPtOYUKTfIooA4V1ZpTVYV16JtWuK84z"; protected-headers="v1" From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= To: Julien Grall , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Stefano Stabellini Message-ID: <969f1492-764b-3345-eb65-64aca554ce9e@suse.com> Subject: Re: [PATCH 7/7] xen/evtchn: read producer index only once References: <20210206104932.29064-1-jgross@suse.com> <20210206104932.29064-8-jgross@suse.com> <8032d8a9-b28f-95e1-a5a8-e955ada4dc0a@xen.org> In-Reply-To: <8032d8a9-b28f-95e1-a5a8-e955ada4dc0a@xen.org> --EKPtOYUKTfIooA4V1ZpTVYV16JtWuK84z Content-Type: multipart/mixed; boundary="------------182073CD3ED7DAC9C47D0BBB" Content-Language: en-US This is a multi-part message in MIME format. --------------182073CD3ED7DAC9C47D0BBB Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 08.02.21 12:40, Julien Grall wrote: >=20 >=20 > On 06/02/2021 10:49, Juergen Gross wrote: >> In evtchn_read() use READ_ONCE() for reading the producer index in >> order to avoid the compiler generating multiple accesses. >> >> Signed-off-by: Juergen Gross >> --- >> =C2=A0 drivers/xen/evtchn.c | 2 +- >> =C2=A0 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c >> index 421382c73d88..f6b199b597bf 100644 >> --- a/drivers/xen/evtchn.c >> +++ b/drivers/xen/evtchn.c >> @@ -211,7 +211,7 @@ static ssize_t evtchn_read(struct file *file, char= =20 >> __user *buf, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 goto unlock_out; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 c =3D u->ring_c= ons; >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 p =3D u->ring_prod; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 p =3D READ_ONCE(u->ring_pr= od); > For consistency, don't you also need the write side in=20 > evtchn_interrupt() to use WRITE_ONCE()? Only in case I'd consider the compiler needing multiple memory accesses for doing the update (see my reply to Jan's comment on this patch). Juergen --------------182073CD3ED7DAC9C47D0BBB Content-Type: application/pgp-keys; name="OpenPGP_0xB0DE9DD628BF132F.asc" Content-Transfer-Encoding: quoted-printable Content-Disposition: attachment; filename="OpenPGP_0xB0DE9DD628BF132F.asc" -----BEGIN PGP PUBLIC KEY BLOCK----- xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOBy= cWx w3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJvedYm8O= f8Z d621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJNwQpd369y= 9bf IhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvxXP3FAp2pkW0xq= G7/ 377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEBAAHNHEp1ZXJnZW4gR= 3Jv c3MgPGpnQHBmdXBmLm5ldD7CwHkEEwECACMFAlOMcBYCGwMHCwkIBwMCAQYVCAIJCgsEFgIDA= QIe AQIXgAAKCRCw3p3WKL8TL0KdB/93FcIZ3GCNwFU0u3EjNbNjmXBKDY4FUGNQH2lvWAUy+dnyT= hpw dtF/jQ6j9RwE8VP0+NXcYpGJDWlNb9/JmYqLiX2Q3TyevpB0CA3dbBQp0OW0fgCetToGIQrg0= MbD 1C/sEOv8Mr4NAfbauXjZlvTj30H2jO0u+6WGM6nHwbh2l5O8ZiHkH32iaSTfN7Eu5RnNVUJbv= oPH Z8SlM4KWm8rG+lIkGurqqu5gu8q8ZMKdsdGC4bBxdQKDKHEFExLJK/nRPFmAuGlId1E3fe10v= 5QL +qHI3EIPtyfE7i9Hz6rVwi7lWKgh7pe0ZvatAudZ+JNIlBKptb64FaiIOAWDCx1SzR9KdWVyZ= 2Vu IEdyb3NzIDxqZ3Jvc3NAc3VzZS5jb20+wsB5BBMBAgAjBQJTjHCvAhsDBwsJCAcDAgEGFQgCC= QoL BBYCAwECHgECF4AACgkQsN6d1ii/Ey/HmQf/RtI7kv5A2PS4RF7HoZhPVPogNVbC4YA6lW7Dr= Wf0 teC0RR3MzXfy6pJ+7KLgkqMlrAbN/8Dvjoz78X+5vhH/rDLa9BuZQlhFmvcGtCF8eR0T1v0nC= /nu AFVGy+67q2DH8As3KPu0344TBDpAvr2uYM4tSqxK4DURx5INz4ZZ0WNFHcqsfvlGJALDeE0Lh= ITT d9jLzdDad1pQSToCnLl6SBJZjDOX9QQcyUigZFtCXFst4dlsvddrxyqT1f17+2cFSdu7+ynLm= XBK 7abQ3rwJY8SbRO2iRulogc5vr/RLMMlscDAiDkaFQWLoqHHOdfO9rURssHNN8WkMnQfvUewRz= 80h SnVlcmdlbiBHcm9zcyA8amdyb3NzQG5vdmVsbC5jb20+wsB5BBMBAgAjBQJTjHDXAhsDBwsJC= AcD AgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey8PUQf/ehmgCI9jB9hlgexLvgOtf7PJn= FOX gMLdBQgBlVPO3/D9R8LtF9DBAFPNhlrsfIG/SqICoRCqUcJ96Pn3P7UUinFG/I0ECGF4EvTE1= jnD kfJZr6jrbjgyoZHiw/4BNwSTL9rWASyLgqlA8u1mf+c2yUwcGhgkRAd1gOwungxcwzwqgljf0= N51 N5JfVRHRtyfwq/ge+YEkDGcTU6Y0sPOuj4Dyfm8fJzdfHNQsWq3PnczLVELStJNdapwPOoE+l= otu fe3AM2vAEYJ9rTz3Cki4JFUsgLkHFqGZarrPGi1eyQcXeluldO3m91NK/1xMI3/+8jbO0tsn1= tqS EUGIJi7ox80eSnVlcmdlbiBHcm9zcyA8amdyb3NzQHN1c2UuZGU+wsB5BBMBAgAjBQJTjHDrA= hsD BwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey+LhQf9GL45eU5vOowA2u5N3= g3O ZUEBmDHVVbqMtzwlmNC4k9Kx39r5s2vcFl4tXqW7g9/ViXYuiDXb0RfUpZiIUW89siKrkzmQ5= dM7 wRqzgJpJwK8Bn2MIxAKArekWpiCKvBOB/Cc+3EXE78XdlxLyOi/NrmSGRIov0karw2RzMNOu5= D+j LRZQd1Sv27AR+IP3I8U4aqnhLpwhK7MEy9oCILlgZ1QZe49kpcumcZKORmzBTNh30FVKK1Evm= V2x AKDoaEOgQB4iFQLhJCdP1I5aSgM5IVFdn7v5YgEYuJYx37IoN1EblHI//x/e2AaIHpzK5h88N= Eaw QsaNRpNSrcfbFmAg987ATQRTjHAWAQgAyzH6AOODMBjgfWE9VeCgsrwH3exNAU32gLq2xvjpW= nHI s98ndPUDpnoxWQugJ6MpMncr0xSwFmHEgnSEjK/PAjppgmyc57BwKII3sV4on+gDVFJR6Y8ZR= wgn BC5mVM6JjQ5xDk8WRXljExRfUX9pNhdE5eBOZJrDRoLUmmjDtKzWaDhIg/+1Hzz93X4fCQkNV= bVF LELU9bMaLPBG/x5q4iYZ2k2ex6d47YE1ZFdMm6YBYMOljGkZKwYde5ldM9mo45mmwe0icXKLk= pEd IXKTZeKDO+Hdv1aqFuAcccTg9RXDQjmwhC3yEmrmcfl0+rPghO0Iv3OOImwTEe4co3c1mwARA= QAB wsBfBBgBAgAJBQJTjHAWAhsMAAoJELDendYovxMvQ/gH/1ha96vm4P/L+bQpJwrZ/dneZcmEw= Tbe 8YFsw2V/Buv6Z4Mysln3nQK5ZadD534CF7TDVft7fC4tU4PONxF5D+/tvgkPfDAfF77zy2AH1= vJz Q1fOU8lYFpZXTXIHb+559UqvIB8AdgR3SAJGHHt4RKA0F7f5ipYBBrC6cyXJyyoprT10EMvU8= VGi wXvTyJz3fjoYsdFzpWPlJEBRMedCot60g5dmbdrZ5DWClAr0yau47zpWj3enf1tLWaqcsuylW= svi uGjKGw7KHQd3bxALOknAp4dN3QwBYCKuZ7AddY9yjynVaD5X7nF9nO5BjR/i1DG86lem3iBDX= zXs ZDn8R38=3D =3D2wuH -----END PGP PUBLIC KEY BLOCK----- --------------182073CD3ED7DAC9C47D0BBB-- --EKPtOYUKTfIooA4V1ZpTVYV16JtWuK84z-- --MibTRswBhznEAVzFPSZwv0FK78kpDjPYj Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmAhJSEFAwAAAAAACgkQsN6d1ii/Ey/t IQgAlW5KCjM05LLQruIcKBrHgQ5NuFxq66+eb2SrqfgpvWigxbqzU0bKA3bJpvuViEdFGtIS1v75 8hnne4C8he9/V0ZBINTvSrtoSN25SBO//r4dVZmUALU+ONiFzIgK0N6QZ/o/anU+sj3gxrFvdYez CatX6TQ1io16ySb0ww2r2DfE9EWMMFYs8+Ojmr5b67iBlPfKnRmSK4F9TrixDmWTmCnm716g6P5x uz80mZj4jRSZ4710JvTJTHepFEioW3TIpnBnrj1eaDUW3aWuMjkn25BKkHq8S/6i9OFW8Bjfifpt XaSEPh2/CrVpmfVYfitd99iMEK8i/4tQjsKZgx8Kjg== =V7sO -----END PGP SIGNATURE----- --MibTRswBhznEAVzFPSZwv0FK78kpDjPYj--