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Mon, 24 Feb 2020 12:18:39 +0100 (CET) Received: from kaod.org (lns-bzn-46-82-253-208-248.adsl.proxad.net [82.253.208.248]) (Authenticated sender: groug@kaod.org) by player715.ha.ovh.net (Postfix) with ESMTPSA id AAB11F829FE3; Mon, 24 Feb 2020 11:18:30 +0000 (UTC) Date: Mon, 24 Feb 2020 12:18:27 +0100 From: Greg Kurz To: David Gibson Subject: Re: [PATCH] spapr: Rework hash<->radix transitions at CAS Message-ID: <20200224121827.59f85580@bahia.home> In-Reply-To: <20200218232105.GG1764@umbus.fritz.box> References: <158160831807.3339719.7059822505220975954.stgit@bahia.lan> <20200213222835.GG124369@umbus.fritz.box> <20200214191900.7e4f91fc@bahia.lan> <20200218232105.GG1764@umbus.fritz.box> X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: multipart/signed; boundary="Sig_/zW3.meU.GWePijvInP=YCFy"; protocol="application/pgp-signature"; micalg=pgp-sha256 X-Ovh-Tracer-Id: 12758416272353958374 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedugedrledtgddviecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpeffhffvuffkjghfofggtgesghdtreerredtvdenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecukfhppedtrddtrddtrddtpdekvddrvdehfedrvddtkedrvdegkeenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhhouggvpehsmhhtphdqohhuthdphhgvlhhopehplhgrhigvrhejudehrdhhrgdrohhvhhdrnhgvthdpihhnvghtpedtrddtrddtrddtpdhmrghilhhfrhhomhepghhrohhugheskhgrohgurdhorhhgpdhrtghpthhtohepqhgvmhhuqdguvghvvghlsehnohhnghhnuhdrohhrgh X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 46.105.72.44 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexey Kardashevskiy , Laurent Vivier , qemu-ppc@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Sig_/zW3.meU.GWePijvInP=YCFy Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 19 Feb 2020 10:21:05 +1100 David Gibson wrote: > On Fri, Feb 14, 2020 at 07:19:00PM +0100, Greg Kurz wrote: > > On Fri, 14 Feb 2020 09:28:35 +1100 > > David Gibson wrote: > >=20 > > > On Thu, Feb 13, 2020 at 04:38:38PM +0100, Greg Kurz wrote: > > > > Until the CAS negotiation is over, an HPT can be allocated on three > > > > different paths: > > > >=20 > > > > 1) during machine reset if the host doesn't support radix, > > > >=20 > > > > 2) during CAS if the guest wants hash and doesn't support HPT resiz= ing, > > > > in which case we pre-emptively resize the HPT to accomodate maxr= am, > > > >=20 > > > > 3) during CAS if no CAS reboot was requested, the guest wants hash = but > > > > we're currently configured for radix. > > > >=20 > > > > Depending on the various combinations of host or guest MMU support, > > > > HPT resizing guest support and the possibility of a CAS reboot, it > > > > is quite hard to know which of these allocates the HPT that will > > > > be ultimately used by the guest that wants to do hash. Also, some of > > > > them have bugs: > > > >=20 > > > > - 2) calls spapr_reallocate_hpt() instead of spapr_setup_hpt_and_vr= ma() > > > > and thus doesn't update the VRMA size, even though we've just ext= ended > > > > the HPT. Not sure what issues this can cause, > > > >=20 > > > > - 3) doesn't check for HPT resizing support and will always allocat= e a > > > > small HPT based on the initial RAM size. This caps the total amou= nt of > > > > RAM the guest can see, especially if maxram is much higher than t= he > > > > initial ram. > > > >=20 > > > > We only support guests that do CAS and we already assume that the H= PT > > > > isn't being used when we do the pre-emptive resizing at CAS. It thus > > > > seems reasonable to only allocate the HPT at the end of CAS, when no > > > > CAS reboot was requested. > > > >=20 > > > > Consolidate the logic so that we only create the HPT during 3), ie. > > > > when we're done with the CAS reboot cycles, and ensure HPT resizing > > > > is taken into account. This fixes the radix->hash transition for > > > > all cases. > > >=20 > > > Uh.. I'm pretty sure this can't work for KVM on a POWER8 host. We > > > need the HPT at all times there, or there's nowhere to put VRMA > > > entries, so we can't run even in real mode. > > >=20 > >=20 > > Well it happens to be working anyway because KVM automatically > > creates an HPT (default size 16MB) in kvmppc_hv_setup_htab_rma() > > if QEMU didn't do so already... Would a comment to emphasize this > > be enough or do you prefer I don't drop the HPT allocation currently > > performed at machine reset ? >=20 > Relying on the automatic allocation is not a good idea. With host > kernels before HPT resizing, once that automatic allocation happens, > we can't change the HPT size *at all*, even with a reset or CAS. >=20 Ah ok I see. With these older host kernels, we need QEMU to allocate the HPT to fit ms->maxram_size, which KVM doesn't know about, or we'll have troubles with VMs that would need a bigger HPT. And I guess we want to support bigger VMs with pre-4.11 host kernels. > So, yes, the current code is annoyingly complex, but it's that way for > a reason. >=20 My motivation here is to get rid of CAS reboot... it definitely needs more thinking on my side. > > > > The guest can theoretically call CAS several times, without a CAS > > > > reboot in between. Linux guests don't do that, but better safe than > > > > sorry, let's ensure we can also handle the symmetrical hash->radix > > > > transition correctly: free the HPT and set the GR bit in PATE. > > > > An helper is introduced for the latter since this is already what > > > > we do during machine reset when going for radix. > > > >=20 > > > > As a bonus, this removes one user of spapr->cas_reboot, which we > > > > want to get rid of in the future. > > > >=20 > > > > Signed-off-by: Greg Kurz > > > > --- > > > > hw/ppc/spapr.c | 25 +++++++++++++++----- > > > > hw/ppc/spapr_hcall.c | 59 ++++++++++++++++++++----------------= ------------ > > > > include/hw/ppc/spapr.h | 1 + > > > > 3 files changed, 44 insertions(+), 41 deletions(-) > > > >=20 > > > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > > > > index 828e2cc1359a..88bc0e4e3ca1 100644 > > > > --- a/hw/ppc/spapr.c > > > > +++ b/hw/ppc/spapr.c > > > > @@ -1573,9 +1573,19 @@ void spapr_setup_hpt_and_vrma(SpaprMachineSt= ate *spapr) > > > > { > > > > int hpt_shift; > > > > =20 > > > > + /* > > > > + * HPT resizing is a bit of a special case, because when enabl= ed > > > > + * we assume an HPT guest will support it until it says it > > > > + * doesn't, instead of assuming it won't support it until it s= ays > > > > + * it does. Strictly speaking that approach could break for > > > > + * guests which don't make a CAS call, but those are so old we > > > > + * don't care about them. Without that assumption we'd have to > > > > + * make at least a temporary allocation of an HPT sized for max > > > > + * memory, which could be impossibly difficult under KVM HV if > > > > + * maxram is large. > > > > + */ > > > > if ((spapr->resize_hpt =3D=3D SPAPR_RESIZE_HPT_DISABLED) > > > > - || (spapr->cas_reboot > > > > - && !spapr_ovec_test(spapr->ov5_cas, OV5_HPT_RESIZE))) { > > > > + || !spapr_ovec_test(spapr->ov5_cas, OV5_HPT_RESIZE)) { > > > > hpt_shift =3D spapr_hpt_shift_for_ramsize(MACHINE(spapr)->= maxram_size); > > > > } else { > > > > uint64_t current_ram_size; > > > > @@ -1604,6 +1614,12 @@ static int spapr_reset_drcs(Object *child, v= oid *opaque) > > > > return 0; > > > > } > > > > =20 > > > > +void spapr_reset_patb_entry(SpaprMachineState *spapr) > > > > +{ > > > > + spapr->patb_entry =3D PATE1_GR; > > > > + spapr_set_all_lpcrs(LPCR_HR | LPCR_UPRT, LPCR_HR | LPCR_UPRT); > > > > +} > > > > + > > > > static void spapr_machine_reset(MachineState *machine) > > > > { > > > > SpaprMachineState *spapr =3D SPAPR_MACHINE(machine); > > > > @@ -1624,10 +1640,7 @@ static void spapr_machine_reset(MachineState= *machine) > > > > * without a HPT because KVM will start them in radix mode. > > > > * Set the GR bit in PATE so that we know there is no HPT. > > > > */ > > > > - spapr->patb_entry =3D PATE1_GR; > > > > - spapr_set_all_lpcrs(LPCR_HR | LPCR_UPRT, LPCR_HR | LPCR_UP= RT); > > > > - } else { > > > > - spapr_setup_hpt_and_vrma(spapr); > > > > + spapr_reset_patb_entry(spapr); > > > > } > > > > =20 > > > > qemu_devices_reset(); > > > > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c > > > > index b8bb66b5c0d4..57ddf0fa6d05 100644 > > > > --- a/hw/ppc/spapr_hcall.c > > > > +++ b/hw/ppc/spapr_hcall.c > > > > @@ -1677,6 +1677,7 @@ static target_ulong h_client_architecture_sup= port(PowerPCCPU *cpu, > > > > bool raw_mode_supported =3D false; > > > > bool guest_xive; > > > > CPUState *cs; > > > > + int maxshift =3D spapr_hpt_shift_for_ramsize(MACHINE(spapr)->m= axram_size); > > > > =20 > > > > /* CAS is supposed to be called early when only the boot vCPU = is active. */ > > > > CPU_FOREACH(cs) { > > > > @@ -1739,36 +1740,6 @@ static target_ulong h_client_architecture_su= pport(PowerPCCPU *cpu, > > > > =20 > > > > guest_xive =3D spapr_ovec_test(ov5_guest, OV5_XIVE_EXPLOIT); > > > > =20 > > > > - /* > > > > - * HPT resizing is a bit of a special case, because when enabl= ed > > > > - * we assume an HPT guest will support it until it says it > > > > - * doesn't, instead of assuming it won't support it until it s= ays > > > > - * it does. Strictly speaking that approach could break for > > > > - * guests which don't make a CAS call, but those are so old we > > > > - * don't care about them. Without that assumption we'd have to > > > > - * make at least a temporary allocation of an HPT sized for max > > > > - * memory, which could be impossibly difficult under KVM HV if > > > > - * maxram is large. > > > > - */ > > > > - if (!guest_radix && !spapr_ovec_test(ov5_guest, OV5_HPT_RESIZE= )) { > > > > - int maxshift =3D spapr_hpt_shift_for_ramsize(MACHINE(spapr= )->maxram_size); > > > > - > > > > - if (spapr->resize_hpt =3D=3D SPAPR_RESIZE_HPT_REQUIRED) { > > > > - error_report( > > > > - "h_client_architecture_support: Guest doesn't supp= ort HPT resizing, but resize-hpt=3Drequired"); > > > > - exit(1); > > > > - } > > > > - > > > > - if (spapr->htab_shift < maxshift) { > > > > - /* Guest doesn't know about HPT resizing, so we > > > > - * pre-emptively resize for the maximum permitted RAM.= At > > > > - * the point this is called, nothing should have been > > > > - * entered into the existing HPT */ > > > > - spapr_reallocate_hpt(spapr, maxshift, &error_fatal); > > > > - push_sregs_to_kvm_pr(spapr); > > > > - } > > > > - } > > > > - > > > > /* NOTE: there are actually a number of ov5 bits where input f= rom the > > > > * guest is always zero, and the platform/QEMU enables them in= dependently > > > > * of guest input. To model these properly we'd want some sort= of mask, > > > > @@ -1806,6 +1777,12 @@ static target_ulong h_client_architecture_su= pport(PowerPCCPU *cpu, > > > > error_report("Guest requested unavailable MMU mode (ha= sh)."); > > > > exit(EXIT_FAILURE); > > > > } > > > > + if (spapr->resize_hpt =3D=3D SPAPR_RESIZE_HPT_REQUIRED && > > > > + !spapr_ovec_test(ov5_guest, OV5_HPT_RESIZE)) { > > > > + error_report( > > > > + "h_client_architecture_support: Guest doesn't supp= ort HPT resizing, but resize-hpt=3Drequired"); > > > > + exit(1); > > > > + } > > > > } > > > > spapr->cas_pre_isa3_guest =3D !spapr_ovec_test(ov1_guest, OV1_= PPC_3_00); > > > > spapr_ovec_cleanup(ov1_guest); > > > > @@ -1838,11 +1815,23 @@ static target_ulong h_client_architecture_s= upport(PowerPCCPU *cpu, > > > > void *fdt; > > > > SpaprDeviceTreeUpdateHeader hdr =3D { .version_id =3D 1 }; > > > > =20 > > > > - /* If spapr_machine_reset() did not set up a HPT but one i= s necessary > > > > - * (because the guest isn't going to use radix) then set i= t up here. */ > > > > - if ((spapr->patb_entry & PATE1_GR) && !guest_radix) { > > > > - /* legacy hash or new hash: */ > > > > - spapr_setup_hpt_and_vrma(spapr); > > > > + if (!guest_radix) { > > > > + /* > > > > + * Either spapr_machine_reset() did not set up a HPT b= ut one > > > > + * is necessary (because the guest isn't going to use = radix), > > > > + * or the guest doesn't know about HPT resizing and we= need to > > > > + * pre-emptively resize for the maximum permitted RAM.= Set it > > > > + * up here. At the point this is called, nothing shoul= d have > > > > + * been entered into the existing HPT. > > > > + */ > > > > + if (spapr->patb_entry & PATE1_GR || spapr->htab_shift = < maxshift) { > > > > + /* legacy hash or new hash: */ > > > > + spapr_setup_hpt_and_vrma(spapr); > > > > + push_sregs_to_kvm_pr(spapr); > > > > + } > > > > + } else { > > > > + spapr_free_hpt(spapr); > > > > + spapr_reset_patb_entry(spapr); > > > > } > > > > =20 > > > > if (fdt_bufsize < sizeof(hdr)) { > > > > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h > > > > index 09110961a589..9d88b5596481 100644 > > > > --- a/include/hw/ppc/spapr.h > > > > +++ b/include/hw/ppc/spapr.h > > > > @@ -919,4 +919,5 @@ void spapr_check_pagesize(SpaprMachineState *sp= apr, hwaddr pagesize, > > > > =20 > > > > void spapr_set_all_lpcrs(target_ulong value, target_ulong mask); > > > > hwaddr spapr_get_rtas_addr(void); > > > > +void spapr_reset_patb_entry(SpaprMachineState *spapr); > > > > #endif /* HW_SPAPR_H */ > > > >=20 > > >=20 > >=20 >=20 >=20 >=20 --Sig_/zW3.meU.GWePijvInP=YCFy Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEtIKLr5QxQM7yo0kQcdTV5YIvc9YFAl5TsQMACgkQcdTV5YIv c9a1ohAAm/v5I4UCdmQsJcF1ThxfQT+9mLXlorIRvTW/vC/cTv5wjoM0VYBrSQZc PER2HxKxZyADjCRoM7o9g/AmkkT6TO5P26bOFsKTeDGnEKILcYgetuN1tenvGtxx o+x+YVroexr438gI1L7Jb7zJHCWFJcKBP2abLB+oVXsdCQwJE7feJUnqJpWs8jFt 7Vz39AwYucPrjka2hOgZJsA3NUzIXbhUJiN06+lHVP+3XH4+D4Afe80Xc1e5xghl 4c4ICrJN7HA7+IZVXtDspC+Hri1Ok4E8k/a1vYhu46dG4g9jw/trmAIO+VN059ls rfB3vob2Z1QmlV53UaLEyHLawYVh6wbe4+rtcSAZ8MUiUripdgI2HybtqSuQZ5vz WZM0OBllYa/ckGIlwWP/6ofNhkrzerlUWbtr5sG3T6yWBb9QnzLCzxYygD156cUs ns4Xx8Sox4GKd9BF5xYjZzB+hGLunlv429ljJ5LAKdS2ctD39nU4hYrEhSVc2VBn Aicwzf3Jp7VvluR7znGU6Ck3L0WXGsMTdKhosb/sDm7T693ztpPJYZLYU86pzR2y B6FmkMy0h7GehzSDVFL0RxHYM8/J9Hp0U2ZZ2am3nuhs1vEJJJdkUVlqPT+15H72 b6iNekX/67pya2ieAvWf2Y9HgDtfYZ49tfHYoE9md7xYCUYZUV0= =Qt71 -----END PGP SIGNATURE----- --Sig_/zW3.meU.GWePijvInP=YCFy--