There is no way in EFI to allocate non cacheable memory.
It is possible via the PI specification, so check out:
gDS->SetMemorySpaceAttributes()
Doing this is very tricky as the DXE Core technically will own the GCD entry
you want to change.
I forget the exact sequence that will work, but you need to make sure the page
is free (allocate and free). Then grab ownership with GCD service, and then
change the attribute.
Andrew Fish
On Aug 17, 2012, at 4:47 PM, Melwyn DSouza wrote:
> Thanks all for quick reply..
> Now , how do i allocate something as in
>
> VirtualAlloc(NULL, g_pgsz, _MEM_LARGE_PAGES | MEM_RESERVE | MEM_COMMIT,
> PAGE_EXECUTE_READWRITE | PAGE_NOCACHE);
>
> a PAGE_NOCACHE type memory...
> ok not a virtual but a physical memory of type PAGE_NOCACHE
>
> Thanks,
> Melwyn.
>
> On Fri, Aug 17, 2012 at 3:16 PM, Andrew Fish <af...@apple.com> wrote:
> On Aug 17, 2012, at 2:49 PM, Melwyn DSouza wrote:
>
> > Experts:
> >
> > 1. Is there a way to requested an allocation of memory where i can specify
> > the start address?
> > AllocateReservedZeroPool (g_reqsz);
> > gives me the requested size. I also want to specify that it give me start
> > address
> >
> > like
> > VirtualAlloc((LPVOID) req_addr, g_reqsz, _MEM_LARGE_PAGES | MEM_RESERVE |
> > MEM_COMMIT, PAGE_EXECUTE_READWRITE);
> >
> > I want to request a particular address for the allocated memory.
>
> In general not a good idea, but possible.
>
> > How to achieve this?
> >
>
> gBS->AllocatePages (AllocateAddress, EfiBootServicesData , 1, &Memory);
>
> See 6.2 Serivces - Boot Services -> Memory Allocation Services in UEFI 2.3.1
> for more details.
>
>
> > 2. If i allocate using
> > AllocateReservedZeroPool
>
> Also in general not a good idea per UEFI spec.
> Note: UEFI Applications, UEFI Drivers, and UEFI OS Loaders must not allocate
> memory of type EfiReservedMemoryType
>
> Use EfiBootServicesData, unless there is a good reason not to. AKA
> AllocateZeroPool().
>
> > in the RootApp at BSP and then
> > Can i access this memory location from a AP thread, like moving data from
> > the allocated memory to a CPU register in the AP thread function?
> > Allocation is done before the starting the AP. But i want to access this
> > allocated memory in the AP thread function.
> >
>
> EFI is always virtual address == physical address so all processors share the
> same view of memory all the time.
>
> The AP is not a thread it is just a CPU that is not (can never be) running
> EFI. It is dangerous to think of the AP as a thread, as it is really just a
> blob of hardware that can access memory and perform calculations. You send
> the AP work via MpServices protocol and data comes back in a memory buffer.
> Nothing else you could do is MP safe. The insidious thing about MpServices is
> in 99% of the cases the AP worker function is compiled into the EFI
> Application/Driver that is calling MpServices so it is really easy to do
> something that is not MP Safe and not notice until you get some random crash.
>
> So good luck!
>
> Thanks,
>
> Andrew
>
> > thanks,
> > Melwyn.
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