On 12/17/21 15:30, Alexander Bulekov wrote: > On 211217 1458, Philippe Mathieu-Daudé wrote: >> On 12/17/21 04:08, Alexander Bulekov wrote: >>> Here's my shot at fixing dma-reentracy issues. This patch adds a flag to >>> the DeviceState, which is set/checked when we call an accessor >>> associated with the device's IO MRs. >> >> Your approach is exactly what Gerd suggested: >> https://www.mail-archive.com/qemu-devel@nongnu.org/msg831437.html > > Yes - my bad for not searching my mail more carefully.
Well it is not "exactly" the same, but almost. >> >>> The problem, in short, as I understand it: For the vast majority of >>> cases, we want to prevent a device from accessing it's own PIO/MMIO >>> regions over DMA. >>> >>> This patch/solution is based on some assumptions: >>> 1. DMA accesses that hit mmio regions are only dangerous if they end up >>> interacting with memory-regions belonging to the device initiating the >>> DMA. >>> Not dangerous: sdhci_pio->dma_write->e1000_mmio >>> Dangerous: sdhci_pio->dma_write->sdhci_mmio >> >> It doesn't have to be dangerous, see Paolo's example which >> invalidated my previous attempt and forced me to write 24 >> patches in multiples series to keep the "niche" cases working: >> https://www.mail-archive.com/qemu-block@nongnu.org/msg72939.html > > I don't understand what IO accesses this decodes to. This is loading a > picture into VRAM? I'd say "loading a picture into VRAM via the DMA" but am not sure :) This link is helpful: http://petesqbsite.com/sections/tutorials/tutorials/peekpoke.txt
