Re: [kvm-unit-tests PATCH v1 2/2] s390x: sie: ensure guests are aligned to 2GB

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Fri,  3 Nov 2023 07:35:47 +0100
Nico Boehr <nrb@linux.ibm.com> wrote:

[...]

> diff --git a/lib/s390x/sie.c b/lib/s390x/sie.c
> index b44febdeaaac..bd907a0ffefa 100644
> --- a/lib/s390x/sie.c
> +++ b/lib/s390x/sie.c
> @@ -15,6 +15,8 @@
>  #include <asm/page.h>
>  #include <libcflat.h>
>  #include <alloc_page.h>
> +#include <vmalloc.h>
> +#include <sclp.h>
>  
>  void sie_expect_validity(struct vm *vm)
>  {
> @@ -111,6 +113,46 @@ void sie_guest_create(struct vm *vm, uint64_t guest_mem, uint64_t guest_mem_len)
>  	vm->sblk->crycbd = (uint32_t)(uintptr_t)vm->crycb;
>  }
>  
> +/*

/**
  * sie_guest_alloc - Allocate memory [...]

> + * Allocate memory for a guest and map it in virtual address space such that
> + * it is properly aligned.
> + * @guest_size the desired size of the guest in bytes.

 * @guest_size: the desired [...]

> + */

let's try to use a consistent style for comments. in many places we use
the kerneldoc style -- let's stick to that

in the future we should pay more attention to the style, there are
several places where we have __almost__ kerneldoc style.

> +uint8_t *sie_guest_alloc(uint64_t guest_size)
> +{
> +	pgd_t *root;
> +	u8 *guest_phys, *guest_virt;
> +	static unsigned long guest_counter = 1;
> +	unsigned long i;

reverse Christmas tree, please

> +
> +	setup_vm();
> +	root = (pgd_t *)(stctg(1) & PAGE_MASK);
> +
> +	/*
> +	 * Start of guest memory in host virtual space needs to be aligned to
> +	 * 2GB for some environments. It also can't be at 2GB since the memory
> +	 * allocator stores its page_states metadata there.
> +	 * Thus we use the next multiple of 4GB after the end of physical
> +	 * mapping. This also leaves space after end of physical memory so the
> +	 * page immediately after physical memory is guaranteed not to be
> +	 * present.
> +	 */
> +	guest_virt = (uint8_t *)ALIGN(get_ram_size() + guest_counter * 4UL * SZ_1G, SZ_2G);
> +	guest_counter++;
> +
> +	guest_phys = alloc_pages(get_order(guest_size) - 12);
> +	/*
> +	 * Establish a new mapping of the guest memory so it can be 2GB aligned
> +	 * without actually requiring 2GB physical memory.
> +	 */
> +	for (i = 0; i <= guest_size; i += PAGE_SIZE) {

i < guest_size ?

> +		install_page(root, __pa(guest_phys + i), guest_virt + i);
> +	}
> +	memset(guest_virt, 0, guest_size);
> +
> +	return guest_virt;
> +}
> +
>  /* Frees the memory that was gathered on initialization */
>  void sie_guest_destroy(struct vm *vm)
>  {

[...]