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SubjectRe: [PATCH] xen: adjust early dom0 p2m handling to xen hypervisor behavior
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On 05/10/2017 12:08 AM, Juergen Gross wrote:
> When booted as pv-guest the p2m list presented by the Xen is already
> mapped to virtual addresses. In dom0 case the hypervisor might make use
> of 2M- or 1G-pages for this mapping. Unfortunately while being properly
> aligned in virtual and machine address space, those pages might not be
> aligned properly in guest physical address space.

Is this the only place where we shouldn't assume that large page is
properly aligned (in pfn space)?

-boris

>
> So when trying to obtain the guest physical address of such a page
> pud_pfn() and pmd_pfn() must be avoided as those will mask away guest
> physical address bits not being zero in this special case.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> arch/x86/xen/mmu_pv.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 9d9ae6650aa1..7397d8b8459d 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -2025,7 +2025,8 @@ static unsigned long __init xen_read_phys_ulong(phys_addr_t addr)
>
> /*
> * Translate a virtual address to a physical one without relying on mapped
> - * page tables.
> + * page tables. Don't rely on big pages being aligned in (guest) physical
> + * space!
> */
> static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
> {
> @@ -2046,7 +2047,7 @@ static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
> sizeof(pud)));
> if (!pud_present(pud))
> return 0;
> - pa = pud_pfn(pud) << PAGE_SHIFT;
> + pa = pud_val(pud) & PTE_PFN_MASK;
> if (pud_large(pud))
> return pa + (vaddr & ~PUD_MASK);
>
> @@ -2054,7 +2055,7 @@ static phys_addr_t __init xen_early_virt_to_phys(unsigned long vaddr)
> sizeof(pmd)));
> if (!pmd_present(pmd))
> return 0;
> - pa = pmd_pfn(pmd) << PAGE_SHIFT;
> + pa = pmd_val(pmd) & PTE_PFN_MASK;
> if (pmd_large(pmd))
> return pa + (vaddr & ~PMD_MASK);
>

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