Messages in this thread | | | Subject | Re: [PATCH] irqchip/gic-v4.1: Properly lock VPEs when doing a directLPI invalidation | From | Zenghui Yu <> | Date | Tue, 4 Jul 2023 23:42:32 +0800 |
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Hi Marc,
On 2023/7/4 2:54, Marc Zyngier wrote: > On Thu, 29 Jun 2023 15:52:24 +0100, > Zenghui Yu <yuzenghui@huawei.com> wrote: >> >> Hi Marc, >> >> Nit: I think the Subject header can be changed to 'irqchip/gic-v4' as >> the bug it fixes only affects GICv4 HW. v4.1 is unaffected. > > I'm not so sure. > > v4.0 didn't allow direct invalidation of VPE doorbells (we had to use > the fake device hack), except for the HiSi special that implemented > DirectLPI despite the presence of multiple ITSs. It was a violation of > the architecture, but it really saved the day by making invalidations > cheap enough.
[ I should've mentioned that I had reproduced the bug and tested your patch on my 920, which is, yeah, a HiSi implementation of GICv4.0 with DirectLPI supported. But ]
> > Only with v4.1 did we get architectural support for doorbell > invalidation via a register instead of a command for a fake device. > > So as far as the architecture is concerned, this should only affect > v4.1. As a side effect, it also affect HiSi's v4.0 implementations.
... iiuc the bug we're fixing is that we perform a register based invalidation for doorbells (via its_vpe_[un]mask_irq/its_vpe_send_inv), acquire and release the per-RD lock with a *race* against a concurrent its_map_vm(), which would modify the vpe->col_idx behind our backs and affect the lock we're looking for.
its_vpe_[un]mask_irq() are callbacks for the v4.0 irqchip, i.e., its_vpe_irq_chip.
With v4.1, we switch to use its_vpe_4_1_irq_chip and invalidate doorbells by sending the new INVDB command (and shouldn't be affected by this bug).
Thanks, Zenghui
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