PVOID NTAPI MmAllocateNonCachedMemory ( IN SIZE_T NumberOfBytes )
Definition at line 25 of file ncache.c.
{
    PFN_COUNT PageCount, MdlPageCount;
    PFN_NUMBER PageFrameIndex;
    PHYSICAL_ADDRESS LowAddress, HighAddress, SkipBytes;
    MI_PFN_CACHE_ATTRIBUTE CacheAttribute;
    PMDL Mdl;
    PVOID BaseAddress;
    PPFN_NUMBER MdlPages;
    PMMPTE PointerPte;
    MMPTE TempPte;

    //
    // Get the page count
    //
    ASSERT(NumberOfBytes != 0);
    PageCount = (PFN_COUNT)BYTES_TO_PAGES(NumberOfBytes);

    //
    // Use the MDL allocator for simplicity, so setup the parameters
    //
    LowAddress.QuadPart = 0;
    HighAddress.QuadPart = -1;
    SkipBytes.QuadPart = 0;
    CacheAttribute = MiPlatformCacheAttributes[0][MmNonCached];

    //
    // Now call the MDL allocator
    //
    Mdl = MiAllocatePagesForMdl(LowAddress,
                                HighAddress,
                                SkipBytes,
                                NumberOfBytes,
                                CacheAttribute,
                                0);
    if (!Mdl) return NULL;

    //
    // Get the MDL VA and check how many pages we got (could be partial)
    //
    BaseAddress = (PVOID)((ULONG_PTR)Mdl->StartVa + Mdl->ByteOffset);
    MdlPageCount = ADDRESS_AND_SIZE_TO_SPAN_PAGES(BaseAddress, Mdl->ByteCount);
    if (PageCount != MdlPageCount)
    {
        //
        // Unlike MDLs, partial isn't okay for a noncached allocation, so fail
        //
        ASSERT(PageCount > MdlPageCount);
        MmFreePagesFromMdl(Mdl);
        ExFreePool(Mdl);
        return NULL;
    }

    //
    // Allocate system PTEs for the base address
    // We use an extra page to store the actual MDL pointer for the free later
    //
    PointerPte = MiReserveSystemPtes(PageCount + 1, SystemPteSpace);
    if (!PointerPte)
    {
        //
        // Out of memory...
        //
        MmFreePagesFromMdl(Mdl);
        ExFreePool(Mdl);
        return NULL;
    }

    //
    // Store the MDL pointer
    //
    *(PMDL*)PointerPte++ = Mdl;

    //
    // Okay, now see what range we got
    //
    BaseAddress = MiPteToAddress(PointerPte);

    //
    // This is our array of pages
    //
    MdlPages = (PPFN_NUMBER)(Mdl + 1);

    //
    // Setup the template PTE
    //
    TempPte = ValidKernelPte;

    //
    // Now check what kind of caching we should use
    //
    switch (CacheAttribute)
    {
        case MiNonCached:

            //
            // Disable caching
            //
            MI_PAGE_DISABLE_CACHE(&TempPte);
            MI_PAGE_WRITE_THROUGH(&TempPte);
            break;

        case MiWriteCombined:

            //
            // Enable write combining
            //
            MI_PAGE_DISABLE_CACHE(&TempPte);
            MI_PAGE_WRITE_COMBINED(&TempPte);
            break;

        default:
            //
            // Nothing to do
            //
            break;
    }

    //
    // Now loop the MDL pages
    //
    do
    {
        //
        // Get the PFN
        //
        PageFrameIndex = *MdlPages++;

        //
        // Set the PFN in the page and write it
        //
        TempPte.u.Hard.PageFrameNumber = PageFrameIndex;
        MI_WRITE_VALID_PTE(PointerPte++, TempPte);
    } while (--PageCount);

    //
    // Return the base address
    //
    return BaseAddress;

}
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