[Xen-devel] Re: [PATCH 2/2] Linux support for hugepages as a Xen PV guest

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 10/10/08 14:30, "dcm@xxxxxxxx" <dcm@xxxxxxxx> wrote:

> This patch adds support to Linux for hugepages as a Xen guest.  It is
> against the linux-2.6.18-xen on xenbits.xensource.com.
> 
> It currently assumes that the guest memory is physically aligned and
> contiguous.  Detection and avoidance of non-aligned memory will be
> available in a future patch.
> 
> Signed-off-by: Dave McCracken <dave.mccracken@xxxxxxxxxx>

hugetlbfs should only be enabled at runtime if supported by the hypervisor.
Perhaps we can enable the PSE CPUID flag if the hypervisor supports
superpages?

> --- linux-2.6.18-xen//./mm/hugetlb.c 2008-07-17 09:54:19.000000000 -0500
> +++ linux-hpage/./mm/hugetlb.c 2008-10-02 15:07:54.000000000 -0500
> @@ -294,12 +294,14 @@ static pte_t make_huge_pte(struct vm_are
> int writable)
>  {
> pte_t entry;
> + pgprot_t pgprot;
>  
> + pgprot = __pgprot(pgprot_val(vma->vm_page_prot) | _PAGE_PRESENT);
> if (writable) {
> entry =
> -      pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
> +      pte_mkwrite(pte_mkdirty(mk_pte(page, pgprot)));
> } else {
> -  entry = pte_wrprotect(mk_pte(page, vma->vm_page_prot));
> +  entry = pte_wrprotect(mk_pte(page, pgprot));
> }
> entry = pte_mkyoung(entry);
> entry = pte_mkhuge(entry);

Why do we need to do something different for Xen here?

 -- Keir



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