[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] [RFC] vpci: allow BAR write while mapped
On 14.03.2025 09:21, Roger Pau Monné wrote: > On Fri, Mar 14, 2025 at 09:04:55AM +0100, Jan Beulich wrote: >> On 13.03.2025 18:48, Roger Pau Monné wrote: >>> On Wed, Mar 12, 2025 at 03:50:17PM -0400, Stewart Hildebrand wrote: >>>> @@ -585,10 +601,31 @@ static void cf_check bar_write( >>>> { >>>> /* If the value written is the current one avoid printing a >>>> warning. */ >>>> if ( val != (uint32_t)(bar->addr >> (hi ? 32 : 0)) ) >>>> + { >>>> gprintk(XENLOG_WARNING, >>>> - "%pp: ignored BAR %zu write while mapped\n", >>>> + "%pp: allowing BAR %zu write while mapped\n", >>>> &pdev->sbdf, bar - pdev->vpci->header.bars + hi); >>> >>> If Xen now handles BARs writes with memory decoding enabled the >>> message can be removed. It's only purpose was to signal this missing >>> handling. >>> >>>> - return; >>>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock)); >>>> + ASSERT(spin_is_locked(&pdev->vpci->lock)); >>>> + reenable = true; >>>> + cmd = pci_conf_read16(pdev->sbdf, PCI_COMMAND); >>>> + /* >>>> + * Write-while-mapped: unmap the old BAR in p2m. We want this >>>> to >>>> + * finish right away since the deferral machinery only >>>> supports >>>> + * unmap OR map, not unmap-then-remap. Ultimately, it >>>> probably would >>>> + * be better to defer the write-while-mapped case just like >>>> regular >>>> + * BAR writes (but still only allow it for 32-bit BAR writes). >>>> + */ >>>> + /* Disable memory decoding */ >>>> + modify_bars(pdev, cmd & ~PCI_COMMAND_MEMORY, false); >>> >>> I think if the guest explicitly avoids toggling memory decoding Xen >>> should also to the same, and not touch the bit. >> >> For Dom0 I'm inclined to agree, but for DomU-s it may be unsafe to do so. >> (You may have meant it like this, but you said "guest".) > > Sorry, I'm not sure I'm following. For domUs the BAR register write > is not propagated to the hardware, it's just the p2m mappings that > change, and hence it's even safer to not toggle the memory decoding > bit for that case? (as there's no write to the device BAR registers > for domUs). Oh, right. I'm sorry for the noise. Jan
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