[Xen-devel] [RFC 2/6] arm64: vdso: Add support for multiple vDSO data pages

[Boqun Feng <boqun.feng@xxxxxxxxx>]

Split __vdso_abi::vdso_pages into nr_vdso_{data,code}_pages, so that
__setup_additional_pages() could work with multiple vDSO data pages with
the setup from __vdso_init().

Multiple vDSO data pages are required when running in a virtualized
environment, where the cycles read from cntvct at userspace need to
be adjusted with some data from a page maintained by the hypervisor. For
example, the TSC page in Hyper-V.

This is a prerequisite for vDSO support in ARM64 on Hyper-V.

Signed-off-by: Boqun Feng (Microsoft) <boqun.feng@xxxxxxxxx>
---
 arch/arm64/kernel/vdso.c | 43 ++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 354b11e27c07..b9b5ec7a3084 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -50,7 +50,8 @@ struct __vdso_abi {
        const char *name;
        const char *vdso_code_start;
        const char *vdso_code_end;
-       unsigned long vdso_pages;
+       unsigned long nr_vdso_data_pages;
+       unsigned long nr_vdso_code_pages;
        /* Data Mapping */
        struct vm_special_mapping *dm;
        /* Code Mapping */
@@ -101,6 +102,8 @@ static int __vdso_init(enum arch_vdso_type arch_index)
 {
        int i;
        struct page **vdso_pagelist;
+       struct page **vdso_code_pagelist;
+       unsigned long nr_vdso_pages;
        unsigned long pfn;
 
        if (memcmp(vdso_lookup[arch_index].vdso_code_start, "\177ELF", 4)) {
@@ -108,14 +111,18 @@ static int __vdso_init(enum arch_vdso_type arch_index)
                return -EINVAL;
        }
 
-       vdso_lookup[arch_index].vdso_pages = (
+       vdso_lookup[arch_index].nr_vdso_data_pages = 1;
+
+       vdso_lookup[arch_index].nr_vdso_code_pages = (
                        vdso_lookup[arch_index].vdso_code_end -
                        vdso_lookup[arch_index].vdso_code_start) >>
                        PAGE_SHIFT;
 
-       /* Allocate the vDSO pagelist, plus a page for the data. */
-       vdso_pagelist = kcalloc(vdso_lookup[arch_index].vdso_pages + 1,
-                               sizeof(struct page *),
+       nr_vdso_pages = vdso_lookup[arch_index].nr_vdso_data_pages +
+                       vdso_lookup[arch_index].nr_vdso_code_pages;
+
+       /* Allocate the vDSO pagelist. */
+       vdso_pagelist = kcalloc(nr_vdso_pages, sizeof(struct page *),
                                GFP_KERNEL);
        if (vdso_pagelist == NULL)
                return -ENOMEM;
@@ -123,15 +130,17 @@ static int __vdso_init(enum arch_vdso_type arch_index)
        /* Grab the vDSO data page. */
        vdso_pagelist[0] = phys_to_page(__pa_symbol(vdso_data));
 
-
        /* Grab the vDSO code pages. */
        pfn = sym_to_pfn(vdso_lookup[arch_index].vdso_code_start);
 
-       for (i = 0; i < vdso_lookup[arch_index].vdso_pages; i++)
-               vdso_pagelist[i + 1] = pfn_to_page(pfn + i);
+       vdso_code_pagelist = vdso_pagelist +
+                            vdso_lookup[arch_index].nr_vdso_data_pages;
+
+       for (i = 0; i < vdso_lookup[arch_index].nr_vdso_code_pages; i++)
+               vdso_code_pagelist[i] = pfn_to_page(pfn + i);
 
-       vdso_lookup[arch_index].dm->pages = &vdso_pagelist[0];
-       vdso_lookup[arch_index].cm->pages = &vdso_pagelist[1];
+       vdso_lookup[arch_index].dm->pages = vdso_pagelist;
+       vdso_lookup[arch_index].cm->pages = vdso_code_pagelist;
 
        return 0;
 }
@@ -141,26 +150,26 @@ static int __setup_additional_pages(enum arch_vdso_type 
arch_index,
                                    struct linux_binprm *bprm,
                                    int uses_interp)
 {
-       unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
+       unsigned long vdso_base, vdso_text_len, vdso_data_len;
        void *ret;
 
-       vdso_text_len = vdso_lookup[arch_index].vdso_pages << PAGE_SHIFT;
-       /* Be sure to map the data page */
-       vdso_mapping_len = vdso_text_len + PAGE_SIZE;
+       vdso_data_len = vdso_lookup[arch_index].nr_vdso_data_pages << 
PAGE_SHIFT;
+       vdso_text_len = vdso_lookup[arch_index].nr_vdso_code_pages << 
PAGE_SHIFT;
 
-       vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
+       vdso_base = get_unmapped_area(NULL, 0,
+                                     vdso_data_len + vdso_text_len, 0, 0);
        if (IS_ERR_VALUE(vdso_base)) {
                ret = ERR_PTR(vdso_base);
                goto up_fail;
        }
 
-       ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE,
+       ret = _install_special_mapping(mm, vdso_base, vdso_data_len,
                                       VM_READ|VM_MAYREAD,
                                       vdso_lookup[arch_index].dm);
        if (IS_ERR(ret))
                goto up_fail;
 
-       vdso_base += PAGE_SIZE;
+       vdso_base += vdso_data_len;
        mm->context.vdso = (void *)vdso_base;
        ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
                                       VM_READ|VM_EXEC|
-- 
2.24.0


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