Marking the page tableas pinned without ever actually pinning is was probably an oversight in the first place. The main reason for the change is more subtle, though: The write of the one present entry each here and in the subsequently allocated L2 table engage a code path in the hypervisor which exists only for thought-to-be-broken guests: An mmu- update operation to a page which is neither a page table nor marked writable. The hypervisor merely assumes (or should I say "hopes") that the fact that a writable reference to the page can be obtained means it is okay to actually write to that page in response to such a hypercall.
While there make all involved code and data dependent upon X86_VSYSCALL_EMULATION (some code was already). Signed-off-by: Jan Beulich <[email protected]> --- a/arch/x86/xen/mmu_pv.c +++ b/arch/x86/xen/mmu_pv.c @@ -86,8 +86,10 @@ #include "mmu.h" #include "debugfs.h" +#ifdef CONFIG_X86_VSYSCALL_EMULATION /* l3 pud for userspace vsyscall mapping */ static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss; +#endif /* * Protects atomic reservation decrease/increase against concurrent increases. @@ -791,7 +793,9 @@ static void __init xen_mark_pinned(struc static void __init xen_after_bootmem(void) { static_branch_enable(&xen_struct_pages_ready); +#ifdef CONFIG_X86_VSYSCALL_EMULATION SetPagePinned(virt_to_page(level3_user_vsyscall)); +#endif xen_pgd_walk(&init_mm, xen_mark_pinned, FIXADDR_TOP); } @@ -1761,7 +1765,6 @@ void __init xen_setup_kernel_pagetable(p set_page_prot(init_top_pgt, PAGE_KERNEL_RO); set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO); set_page_prot(level3_kernel_pgt, PAGE_KERNEL_RO); - set_page_prot(level3_user_vsyscall, PAGE_KERNEL_RO); set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO); set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO); set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO); @@ -1778,6 +1781,13 @@ void __init xen_setup_kernel_pagetable(p /* Unpin Xen-provided one */ pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd))); +#ifdef CONFIG_X86_VSYSCALL_EMULATION + /* Pin user vsyscall L3 */ + set_page_prot(level3_user_vsyscall, PAGE_KERNEL_RO); + pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, + PFN_DOWN(__pa_symbol(level3_user_vsyscall))); +#endif + /* * At this stage there can be no user pgd, and no page structure to * attach it to, so make sure we just set kernel pgd.
