From: "ext Kanigeri, Hari" <h-kanigeri2@xxxxxx> Subject: RE: [PATCH 1/4] [OMAPZOOM] DSPBRIDGE: Memory lock for DMM. Date: Wed, 1 Apr 2009 16:58:08 +0200 > Doyu-san, > > > There can be multiple user applications which can do (v)-(p)-(d) > > mapping and these processes can be killed unexpectedly. Even in such a > > case, it would be nice if (p)-(d) mapping could be released without > > restarting a whole iommu. > > > > (v): mpu virtual address > > (p): physicall address > > (d): device virtual address > > -- This patch is not basing on restarting the iommu when a process > is killed unexpectedly. It will just remove the p-d translations of > the Killed process from DSP MMU along with unlocking this buffer > during the Bridge's resource cleanup. What I meant by "vma->vm_ops->close(vma)" was that, if (v)-(p)-(d) mapping can be tied just to some process context in saner manner, I think that we don't have to call "find_task_by_vpid(pCtxtclosed->pid)" explicitly/globally, but automatically it can be cleaned up, when a process is exitting, although I'm not so sure right now;), just guessing... > > Thank you, > Best regards, > Hari > > > -----Original Message----- > > From: Hiroshi DOYU [mailto:Hiroshi.DOYU@xxxxxxxxx] > > Sent: Wednesday, April 01, 2009 9:18 AM > > To: Kanigeri, Hari > > Cc: Pandita, Vikram; linux-omap@xxxxxxxxxxxxxxx; Guzman Lugo, Fernando; > > Menon, Nishanth > > Subject: Re: [PATCH 1/4] [OMAPZOOM] DSPBRIDGE: Memory lock for DMM. > > > > Hi Hari, > > > > From: "ext Kanigeri, Hari" <h-kanigeri2@xxxxxx> > > Subject: RE: [PATCH 1/4] [OMAPZOOM] DSPBRIDGE: Memory lock for DMM. > > Date: Wed, 1 Apr 2009 15:01:29 +0200 > > > > [...] > > > > > > Hm....for this page swapping case, I think that handling this issue in > > > > kernel may cause more complexity and this can be avoided by "mlock()" > > > > for that buffer in userland? This looks more sipmpler? > > > > > > > > > > > > > > > -- I see your point of handling the locking from user-space > > > itself. This can be done in normal Page swapping scenarios, but in > > > the case of abnormal termination of the user-space Process that > > > mapped the buffers we still have an issue. > > > > > > This is what I think the problem might be if we move the locking to > > user-land. > > > - User process mapped and locked the buffer using mlock. > > > - The Physical address mapped to DSP VA by DSPBridge. > > > - The User process got terminated abnormally. I think this > > > will cause the Kernel to reclaim the User buffers that were > > > mapped. > > > - Now the DSP is not aware of this cleanup and it might be > > > still trying to access the Mapped address, but since the Pages > > > are removed we will end up with MMU fault or DSP corrupting > > > the memory of other Processes as the reclaimed Pages might be > > > allocated to other Processes. > > > > > > By moving the locking to Kernel space, we are guaranteed that these > > > Pages are locked even when an application that mapped the buffers is > > > terminated. These Pages will be unlocked only during Bridge's > > > resource cleanup of this Process after Bridge informing the DSP s/w > > > not to access this buffer. > > > > > > I think if the resource cleanup is moved to bridge_release instead > > > of bridge_open, then it might be possible to move the locking > > > mechanism to User land. Here I am assuming that on abnormal > > > termination of a Process, the Kernel first calls the bridge_release > > > on behalf of the Process before reclaiming the buffers that were > > > allocated by this Process otherwise there is a narrow Window when > > > DSP might try to access the memory that is no longer valid. > > > > There can be multiple user applications which can do (v)-(p)-(d) > > mapping and these processes can be killed unexpectedly. Even in such a > > case, it would be nice if (p)-(d) mapping could be released without > > restarting a whole iommu. > > > > (v): mpu virtual address > > (p): physicall address > > (d): device virtual address > > > > So I am considering if "vma->vm_ops->close(vma)" can afford the above > > mechanism. > > > > Hiroshi DOYU > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
