From: Wei Hu <weh@xxxxxxxxxxxxx> Sent: Friday, December 6, 2019 3:32 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.
>
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> Signed-off-by: Wei Hu <weh@xxxxxxxxxxxxx>
> ---
[snip]
> +/*
> + * Allocate enough contiguous physical memory.
> + * Return physical address if succeeded or -1 if failed.
> + */
> +static phys_addr_t hvfb_get_phymem(struct hv_device *hdev,
> + unsigned int request_size)
> +{
> + struct page *page = NULL;
> + dma_addr_t dma_handle;
> + void *vmem;
> + unsigned int request_pages;
> + phys_addr_t paddr = 0;
> + unsigned int order = get_order(request_size);
> +
> + if (request_size == 0)
> + return -1;
> +
> + if (order < MAX_ORDER) {
> + /* Call alloc_pages if the size is less than 2^MAX_ORDER */
> + page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
> + if (!page)
> + return -1;
> +
> + paddr = (page_to_pfn(page) << PAGE_SHIFT);
> + request_pages = (1 << order);
The above line is no longer needed. request_pages was previously an
argument to a pr_info() statement, but that statement has appropriately
been removed.
> + } else {
> + /* Allocate from CMA */
> + hdev->device.coherent_dma_mask = DMA_BIT_MASK(64);
> +
> + request_pages = (round_up(request_size, PAGE_SIZE) >>
> + PAGE_SHIFT);
> +
> + vmem = dma_alloc_coherent(&hdev->device,
> + request_pages * PAGE_SIZE,
> + &dma_handle,
> + GFP_KERNEL | __GFP_NOWARN);
With the request_pages value no longer being needed, there's wasted motion
in doing a PAGE_SHIFT shift to calculate request_pages, and then multiplying by
PAGE_SIZE. The second argument above could just be
round_up(request_size, PAGE_SIZE). Then it would be exactly parallel to
the second argument to dma_free_coherent() below in hvfb_release_phymem().
The request_pages variable can be eliminated entirely.
> +
> + if (!vmem)
> + return -1;
> +
> + paddr = virt_to_phys(vmem);
> + }
> +
> + return paddr;
> +}
> +
> +/* Release contiguous physical memory */
> +static void hvfb_release_phymem(struct hv_device *hdev,
> + phys_addr_t paddr, unsigned int size)
> +{
> + unsigned int order = get_order(size);
> +
> + if (order < MAX_ORDER)
> + __free_pages(pfn_to_page(paddr >> PAGE_SHIFT), order);
> + else
> + dma_free_coherent(&hdev->device,
> + round_up(size, PAGE_SIZE),
> + phys_to_virt(paddr),
> + paddr);
> +}
> +
>
Everything else looks good. The most recent changes to hvfb_getmem() worked
out very nicely.
Michael
