From: "Cédric Le Goater" <email@example.com> To: Ravi Bangoria <firstname.lastname@example.org>, David Gibson <email@example.com> Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH v5 3/3] ppc: Enable 2nd DAWR support on p10 Date: Wed, 21 Apr 2021 08:31:31 +0200 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 4/21/21 8:20 AM, Ravi Bangoria wrote: > Hi David, > > On 4/19/21 10:23 AM, David Gibson wrote: >> On Mon, Apr 12, 2021 at 05:14:33PM +0530, Ravi Bangoria wrote: >>> As per the PAPR, bit 0 of byte 64 in pa-features property indicates >>> availability of 2nd DAWR registers. i.e. If this bit is set, 2nd >>> DAWR is present, otherwise not. Use KVM_CAP_PPC_DAWR1 capability to >>> find whether kvm supports 2nd DAWR or not. If it's supported, allow >>> user to set the pa-feature bit in guest DT using cap-dawr1 machine >>> capability. Though, watchpoint on powerpc TCG guest is not supported >>> and thus 2nd DAWR is not enabled for TCG mode. >>> >>> Signed-off-by: Ravi Bangoria <firstname.lastname@example.org> >>> Reviewed-by: Greg Kurz <email@example.com> >> >> So, I'm actually not sure if using an spapr capability is what we want >> to do here. The problem is that presumably the idea is to at some >> point make the DAWR1 capability default to on (on POWER10, at least). >> But at that point you'll no longer to be able to start TCG guests >> without explicitly disabling it. That's technically correct, since we >> don't implement DAWR1 in TCG, but then we also don't implement DAWR0 >> and we let that slide... which I think is probably going to cause less >> irritation on balance. > > Ok. Probably something like this is what you want? > > Power10 behavior: > - KVM does not support DAWR1: Boot the guest without DAWR1 > support (No warnings). Error out only if user tries with > cap-dawr1=on. > - KVM supports DAWR1: Boot the guest with DAWR1 support, unless > user specifies cap-dawr1=off. > - TCG guest: Ignore cap-dawr1 i.e. boot as if there is only > DAWR0 (Should be fixed in future while adding PowerPC watch- > point support in TCG mode) > > Power10 predecessor behavior: > - KVM guest: Boot the guest without DAWR1 support. Error out > if user tries with cap-dawr1=on. > - TCG guest: Ignore cap-dawr1 i.e. boot as if there is only > DAWR0 (Should be fixed in future while adding PowerPC watch- > point support in TCG mode) > >> I'm wondering if we're actually just better off setting the pa feature >> just based on the guest CPU model. TCG will be broken if you try to >> use it, but then, it already is. AFAIK there's no inherent reason we >> couldn't implement DAWR support in TCG, it's just never been worth the >> trouble. > > Correct. Probably there is no practical usecase for DAWR in TCG mode. What's the expected behavior ? Is it to generate a DSI if we have a DAWR match ? C.
next prev parent reply index Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-12 11:44 [PATCH v5 0/3] ppc: Enable 2nd DAWR support on Power10 Ravi Bangoria 2021-04-12 11:44 ` [PATCH v5 1/3] Linux headers: update from 5.12-rc3 Ravi Bangoria 2021-04-12 11:44 ` [PATCH v5 2/3] ppc: Rename current DAWR macros and variables Ravi Bangoria 2021-04-19 4:47 ` David Gibson 2021-04-12 11:44 ` [PATCH v5 3/3] ppc: Enable 2nd DAWR support on p10 Ravi Bangoria 2021-04-12 13:10 ` Cédric Le Goater 2021-04-19 4:53 ` David Gibson 2021-04-21 6:20 ` Ravi Bangoria 2021-04-21 6:31 ` Cédric Le Goater [this message] 2021-04-21 6:54 ` Ravi Bangoria 2021-04-22 1:56 ` David Gibson 2021-04-22 4:45 ` Richard Henderson 2021-05-05 5:50 ` David Gibson
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