From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: Guest start issue on ARM (maybe related to Credit2) [Was: Re: [xen-unstable test] 113807: regressions - FAIL] Date: Mon, 25 Sep 2017 19:29:17 +0200 Message-ID: <1506360557.27663.15.camel@citrix.com> References: <1506348460.27663.3.camel@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5553373951073732241==" Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" To: Julien Grall , osstest service owner , xen-devel@lists.xensource.com Cc: Stefano Stabellini List-Id: xen-devel@lists.xenproject.org --===============5553373951073732241== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="=-htAQCRkBzqkA1zaynsuo" --=-htAQCRkBzqkA1zaynsuo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2017-09-25 at 17:23 +0100, Julien Grall wrote: > On 09/25/2017 03:07 PM, Dario Faggioli wrote: > > Hey, >=20 > Hi Dario, >=20 Hi! > > I don't see much in the logs, TBH, but both `xl vcpu-list' and the > > 'r' > > debug key seem to suggest that vCPU 0 is running, while the other > > vCPUs > > have never run... like it was an issue with secondary (v)CPU > > bringup. > >=20 > It definitely rings a bell, I have seen similar trace in July and I > have=C2=A0 > been working on a potential fix since then. >=20 > Most of the time guest-start/debian.repeat fails, vCPU 0 is in=C2=A0 > data/prefetch abort state. My guess is a latent cache bug that > credit2=C2=A0 > appears to expose. >=20 > Indeed, the arm32 kernel is using set/way cache flush instruction at=C2= =A0 > boot time. They are used to clean one by one each level of caches on=C2= =A0 > each CPUs. >=20 > At the moment, Xen does not trap those instructions. As you know > cache=C2=A0 > may not be private to a given physical processors. So if you happen > to=C2=A0 > migrate the vCPU to another physical CPU, you may hit stale data. >=20 Ah, yes, I remember "hearing" you talking about this. We've also talked about it a bit together... I just wasn't recognising it being what's biting us here. > I am still cleaning-up my work and hopefully can post a couple of > series=C2=A0 > soon. This is not targeting Xen 4.10 and I am not even sure it would > fix=C2=A0 > the problem here. But that's my best guess. >=20 Well, yes, now that you mention it, it indeed sounds plausible. So, I was mainly curious about whether it was either something which was affecting or directly caused by Credit2, or something that Credit2 can help diagnose, reproduce and fix. Since we already have a candidate, and you're already working on the (difficult! :-( ), well, let's see, once you'll have it, if it actually cures the problem. We'll jump back on it if it does not. Thanks and regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-htAQCRkBzqkA1zaynsuo Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAABCAAGBQJZyTztAAoJEBZCeImluHPuJbMP+wT1ZAAsMYr3yCsd/QCss4Wa +c52tctwpg6IRWMZcqaRSR6neLwLNRIJpsvbnnTaR8xrB1vpttKjR2gjEl7AgR4A 664t5Grkip5cpKJatmp+sj7XAhJsA+4qWaYubnCvFXRIPUygZbcTDvoqMhXjW3vH 9hgLm/Nz9ke66m4Ns2sMRFnyVq+Mgvidy8Fipe08drKr44r4uhkY4pK0uZHPcw8n +n66sKr4puOuHqSWBJ4to4VFG/spC6axfNkEsqNNX8lNZwaA/sHA5WZ78gGzmsTR 2LUaYZ7jedhl/nJ2hZZS2xx68cg5PnZjCM39RD6kW6pJkRH67S0IUVCQ0LwdOH07 u84Nazio0AszqOtUn1gDCwhLtkvp5rdyARcwdU9gFM3GBFgT/x4r3UNBJ0s2Zex4 vPUJhobokQ+GzU0hHKmomIXCfMfTdH+43/t58g6EsnvMC1ttmZY8rnD+lE4GI2IN PgyIDoiSvn4NqbalKwtpyglfXxw6WEOwKFlPCeqdX1/E6gtTRgSWI4RY0vy+SKdR Jp1x0dCqsqNgoG2At5YW4rvLEa2/5GzcDzN+uQzF6Ph7wjiwblpUHSISwcOSRt/7 Hu8cAeyskyGaaN0c6ds4c2uB0gNb0MeDDCHy40m54Mo5VnkTRJy5s3vymbxDhS4L soEL+XQcfNfKw7BbSarU =CxvC -----END PGP SIGNATURE----- --=-htAQCRkBzqkA1zaynsuo-- --===============5553373951073732241== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: inline X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KWGVuLWRldmVs IG1haWxpbmcgbGlzdApYZW4tZGV2ZWxAbGlzdHMueGVuLm9yZwpodHRwczovL2xpc3RzLnhlbi5v cmcveGVuLWRldmVsCg== --===============5553373951073732241==--