From: Wei Hu <weh@xxxxxxxxxxxxx> Sent: Tuesday, October 22, 2019 4:11 AM
>
> On Hyper-V, Generation 1 VMs can directly use VM's physical memory for
> their framebuffers. This can improve the efficiency of framebuffer and
> overall performence for VM. The physical memory assigned to framebuffer
> must be contiguous. We use CMA allocator to get contiguouse physicial
> memory when the framebuffer size is greater than 4MB. For size under
> 4MB, we use alloc_pages to achieve this.
>
> To enable framebuffer memory allocation from CMA, supply a kernel
> parameter to give enough space to CMA allocator at boot time. For
> example:
> cma=130m
> This gives 130MB memory to CAM allocator that can be allocated to
> framebuffer. If this fails, we fall back to the old way of using
> mmio for framebuffer.
>
> Signed-off-by: Wei Hu <weh@xxxxxxxxxxxxx>
> ---
[snip]
> +/*
> + * Allocate enough contiguous physical memory.
> + * Return physical address if succeeded or -1 if failed.
> + */
> +static unsigned long hvfb_get_phymem(unsigned int request_size)
> +{
> + struct page *page = NULL;
> + unsigned int request_pages;
> + unsigned long paddr = 0;
Using 'unsigned long' for physical addresses is problematic on 32-bit
systems with Physical Address Extension (PAE) enabled. Linux has
phys_addr_t that handles 32-bit PAE correctly and that probably
should be used here. This whole driver needs to be carefully
checked for the correct type for physical addresses.
> + unsigned int order = get_order(request_size);
> +
> + if (request_size == 0)
> + return -1;
> +
> + /* Try call alloc_pages if the size is less than 2^MAX_ORDER */
> + if (order < MAX_ORDER) {
> + page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
> + if (!page)
> + return -1;
> +
> + request_pages = (1 << order);
> + goto get_phymem1;
> + }
> +
> + /* Allocate from CMA */
> + // request_pages = (request_size >> PAGE_SHIFT) + 1;
> + request_pages = (round_up(request_size, PAGE_SIZE) >> PAGE_SHIFT);
> + page = dma_alloc_from_contiguous(NULL, request_pages, 0, false);
> +
> + if (page == NULL)
> + return -1;
> +
> +get_phymem1:
> + paddr = (page_to_pfn(page) << PAGE_SHIFT);
> +
> + pr_info("Allocated %d pages starts at physical addr 0x%lx\n",
> + request_pages, paddr);
> +
> + return paddr;
> +}
> +
> +/* Release contiguous physical memory */
> +static void hvfb_release_phymem(unsigned long paddr, unsigned int size)
Same issue here with 'unsigned long paddr'.
> +{
> + unsigned int order = get_order(size);
> +
> + if (order < MAX_ORDER)
> + __free_pages(pfn_to_page(paddr >> PAGE_SHIFT), order);
> + else
> + dma_release_from_contiguous(NULL,
> + pfn_to_page(paddr >> PAGE_SHIFT),
> + (round_up(size, PAGE_SIZE) >>
> + PAGE_SHIFT));
> + // (size >> PAGE_SHIFT) + 1);
> +}
> +
>
> /* Get framebuffer memory from Hyper-V video pci space */
> static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
> @@ -947,8 +1017,58 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
> void __iomem *fb_virt;
> int gen2vm = efi_enabled(EFI_BOOT);
> resource_size_t pot_start, pot_end;
> + unsigned long paddr;
Same issue with 'unsigned long'.
> int ret;
>
> + if (!gen2vm) {
> + pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT,
> + PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
> + if (!pdev) {
> + pr_err("Unable to find PCI Hyper-V video\n");
> + return -ENODEV;
> + }
> + }
> +
> + info->apertures = alloc_apertures(1);
> + if (!info->apertures)
> + goto err1;
> +
> + if (gen2vm) {
> + info->apertures->ranges[0].base = screen_info.lfb_base;
> + info->apertures->ranges[0].size = screen_info.lfb_size;
> + } else {
> + info->apertures->ranges[0].base = pci_resource_start(pdev, 0);
> + info->apertures->ranges[0].size = pci_resource_len(pdev, 0);
> + }
> +
> + /*
> + * For Gen 1 VM, we can directly use the contiguous memory
> + * from VM. If we success, deferred IO happens directly
> + * on this allocated framebuffer memory, avoiding extra
> + * memory copy.
> + */
> + if (!gen2vm) {
> + paddr = hvfb_get_phymem(screen_fb_size);
> + if (paddr != (unsigned long) -1) {
phys_addr_t
> + par->mmio_pp = paddr;
I'm not really sure what to do about the above, because mmio_pp is
declared as 'unsigned long' when it really should be phys_addr_t.
But maybe a MMIO address will always be less than 4 Gb and therefore
will fit in 32 bits?
> + par->mmio_vp = par->dio_vp = __va(paddr);
> +
> + info->fix.smem_start = paddr;
smem_start is also declared as 'unsigned long', which seems
problematic with 32-bit PAE. There are a lot of drivers that cast values
as 'unsigned long' before storing into smem_start
> + info->fix.smem_len = screen_fb_size;
> + info->screen_base = par->mmio_vp;
> + info->screen_size = screen_fb_size;
> +
> + par->need_docopy = false;
> + goto getmem1;
> + } else {
> + pr_info("Unable to allocate enough contiguous physical memory on
> Gen 1 VM. Use MMIO instead.\n");
> + }
> + }
> +
> + /*
> + * Cannot use the contiguous physical memory.
> + * Allocate mmio space for framebuffer.
> + */
> dio_fb_size =
> screen_width * screen_height * screen_depth / 8;
>
> @@ -956,13 +1076,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
> pot_start = 0;
> pot_end = -1;
> } else {
> - pdev = pci_get_device(PCI_VENDOR_ID_MICROSOFT,
> - PCI_DEVICE_ID_HYPERV_VIDEO, NULL);
> - if (!pdev) {
> - pr_err("Unable to find PCI Hyper-V video\n");
> - return -ENODEV;
> - }
> -
> if (!(pci_resource_flags(pdev, 0) & IORESOURCE_MEM) ||
> pci_resource_len(pdev, 0) < screen_fb_size) {
> pr_err("Resource not available or (0x%lx < 0x%lx)\n",
> @@ -991,20 +1104,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info
> *info)
> if (par->dio_vp == NULL)
> goto err3;
>
> - info->apertures = alloc_apertures(1);
> - if (!info->apertures)
> - goto err4;
> -
> - if (gen2vm) {
> - info->apertures->ranges[0].base = screen_info.lfb_base;
> - info->apertures->ranges[0].size = screen_info.lfb_size;
> - remove_conflicting_framebuffers(info->apertures,
> - KBUILD_MODNAME, false);
> - } else {
> - info->apertures->ranges[0].base = pci_resource_start(pdev, 0);
> - info->apertures->ranges[0].size = pci_resource_len(pdev, 0);
> - }
> -
> /* Physical address of FB device */
> par->mmio_pp = par->mem->start;
32-bit PAE problem could also occur here, even though the above line isn't
part of your patch.
Ideally, we would build the kernel in 32-bit mode with PAE enabled, and
test in an environment where the frame buffer gets allocated above the
4 Gbyte line. There may be some similar bugs in other parts of this
driver that aren't touched by the patch.
Michael
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