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Subject[RFC 2/6] arm64: vdso: Add support for multiple vDSO data pages
Date
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@gmail.com>
---
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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