Re: [External] : [PATCH] RISC-V: KVM: Transparent huge page support

[ALOK TIWARI <alok.a.tiwari@oracle.com>]

On 9/28/2025 1:14 PM, liu.xuemei1@zte.com.cn wrote:
> +static bool gstage_supports_huge_mapping(struct kvm_memory_slot *memslot, unsigned long hva)
> +{
> +	gpa_t gpa_start;
> +	hva_t uaddr_start, uaddr_end;
> +	size_t size;
> +
> +	size = memslot->npages * PAGE_SIZE;
> +	uaddr_start = memslot->userspace_addr;
> +	uaddr_end = uaddr_start + size;
> +
> +	gpa_start = memslot->base_gfn << PAGE_SIZE;

looks wrong why << PAGE_SIZE ? typo

> +
> +	/*
> +	 * Pages belonging to memslots that don't have the same alignment
> +	 * within a PMD for userspace and GPA cannot be mapped with g-stage
> +	 * PMD entries, because we'll end up mapping the wrong pages.
> +	 *
> +	 * Consider a layout like the following:
> +	 *
> +	 *    memslot->userspace_addr:
> +	 *    +-----+--------------------+--------------------+---+
> +	 *|abcde|fgh vs-stage block | vs-stage block tv|xyz|
> +	 *    +-----+--------------------+--------------------+---+
> +	 *
> +	 *    memslot->base_gfn << PAGE_SHIFT:
> +	 *      +---+--------------------+--------------------+-----+
> +	 *|abc|def g-stage block | g-stage block |tvxyz|
> +	 *      +---+--------------------+--------------------+-----+
> +	 *
> +	 * If we create those g-stage blocks, we'll end up with this incorrect
> +	 * mapping:
> +	 *   d -> f
> +	 *   e -> g
> +	 *   f -> h
> +	 */
> +	if ((gpa_start & (PMD_SIZE - 1)) != (uaddr_start & (PMD_SIZE - 1)))
> +		return false;
> +
> +	/*
> +	 * Next, let's make sure we're not trying to map anything not covered
> +	 * by the memslot. This means we have to prohibit block size mappings
> +	 * for the beginning and end of a non-block aligned and non-block sized
> +	 * memory slot (illustrated by the head and tail parts of the
> +	 * userspace view above containing pages 'abcde' and 'xyz',
> +	 * respectively).
> +	 *
> +	 * Note that it doesn't matter if we do the check using the
> +	 * userspace_addr or the base_gfn, as both are equally aligned (per
> +	 * the check above) and equally sized.
> +	 */
> +	return (hva >= ALIGN(uaddr_start, PMD_SIZE)) && (hva < ALIGN_DOWN(uaddr_end, PMD_SIZE));
> +}
> +


Thanks,
Alok