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Message-ID: <20230411211343.43b6833a@kernel.org> Date: Tue, 11 Apr 2023 21:13:43 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Roman Gushchin <roman.gushchin@...ux.dev> Cc: Lars-Peter Clausen <lars@...afoo.de>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Rafal Ozieblo <rafalo@...ence.com> Subject: Re: [PATCH net] net: macb: fix a memory corruption in extended buffer descriptor mode On Tue, 11 Apr 2023 20:48:50 -0700 Roman Gushchin wrote: > > diff --git a/drivers/net/ethernet/cadence/macb_main.c > > b/drivers/net/ethernet/cadence/macb_main.c > > index d13fb1d31821..1a40d5a26f36 100644 > > --- a/drivers/net/ethernet/cadence/macb_main.c > > +++ b/drivers/net/ethernet/cadence/macb_main.c > > @@ -1042,6 +1042,10 @@ static dma_addr_t macb_get_addr(struct macb *bp, > > struct macb_dma_desc *desc) > > } > > #endif > > addr |= MACB_BF(RX_WADDR, MACB_BFEXT(RX_WADDR, desc->addr)); > > +#ifdef CONFIG_MACB_USE_HWSTAMP > > + if (bp->hw_dma_cap & HW_DMA_CAP_PTP) > > + addr &= ~GEM_BIT(DMA_RXVALID_OFFSET); > > +#endif > > return addr; > > } > > I think this version is slightly worse because it adds an unconditional > if statement, which can be removed with certain config options. > I can master a version with a helper function, if it's preferable. > > But if you like this one, it's fine too, let me know, I'll send an updated > version. Yup, IMHO this looks better. More likely that someone reading the code will spot the trickiness. I suspect we could clear that bit unconditionally, if the branch is a concern. The code seems to assume that buffers it gets are 8B aligned already, regardless of CONFIG_MACB_USE_HWSTAMP. Drivers commonly save the DMA address to a SW ring (here I think rx_skbuff plays this role but only holds single ptr per entry) so that they don't have to access potentially uncached descriptor ring. But that'd be too large of a change for a fix.
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