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Kernel: Set the G (global) bit for kernel page tables

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Since the kernel page tables are shared between all processes, there's
no need to (implicitly) flush the TLB for them on every context switch.

Setting the G bit on kernel page tables allows the CPU to keep the
translation caches around.
This commit is contained in:
Andreas Kling 2019-11-03 23:40:10 +01:00
parent 4bf1a72d21
commit 5b7f8634e3
2 changed files with 19 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

12
Kernel/Arch/i386/CPU.h
View file

@ -104,6 +104,7 @@ public:
UserSupervisor = 1 << 2,
WriteThrough = 1 << 3,
CacheDisabled = 1 << 4,
Global = 1 << 8,
};
bool is_present() const { return raw() & Present; }
@ -121,7 +122,10 @@ public:
bool is_cache_disabled() const { return raw() & CacheDisabled; }
void set_cache_disabled(bool b) { set_bit(CacheDisabled, b); }
void set_bit(u8 bit, bool value)
bool is_global() const { return raw() & Global; }
void set_global(bool b) { set_bit(Global, b); }
void set_bit(u32 bit, bool value)
{
if (value)
m_raw |= bit;
@ -152,6 +156,7 @@ public:
UserSupervisor = 1 << 2,
WriteThrough = 1 << 3,
CacheDisabled = 1 << 4,
Global = 1 << 8,
};
bool is_present() const { return raw() & Present; }
@ -169,7 +174,10 @@ public:
bool is_cache_disabled() const { return raw() & CacheDisabled; }
void set_cache_disabled(bool b) { set_bit(CacheDisabled, b); }
void set_bit(u8 bit, bool value)
bool is_global() const { return raw() & Global; }
void set_global(bool b) { set_bit(Global, b); }
void set_bit(u32 bit, bool value)
{
if (value)
m_raw |= bit;

9
Kernel/VM/MemoryManager.cpp
View file

@ -158,6 +158,12 @@ void MemoryManager::initialize_paging()
dbgprintf("MM: Installing page directory\n");
#endif
// Turn on CR4.PGE so the CPU will respect the G bit in page tables.
asm volatile(
"mov %cr4, %eax\n"
"orl $0x10, %eax\n"
"mov %eax, %cr4\n");
asm volatile("movl %%eax, %%cr3" ::"a"(kernel_page_directory().cr3()));
asm volatile(
"movl %%cr0, %%eax\n"
@ -187,12 +193,14 @@ PageTableEntry& MemoryManager::ensure_pte(PageDirectory& page_directory, Virtual
pde.set_user_allowed(false);
pde.set_present(true);
pde.set_writable(true);
pde.set_global(true);
} else if (page_directory_index == 1) {
ASSERT(&page_directory == m_kernel_page_directory);
pde.set_page_table_base((u32)m_page_table_one);
pde.set_user_allowed(false);
pde.set_present(true);
pde.set_writable(true);
pde.set_global(true);
} else {
//ASSERT(&page_directory != m_kernel_page_directory.ptr());
auto page_table = allocate_supervisor_physical_page();
@ -210,6 +218,7 @@ PageTableEntry& MemoryManager::ensure_pte(PageDirectory& page_directory, Virtual
pde.set_user_allowed(true);
pde.set_present(true);
pde.set_writable(true);
pde.set_global(&page_directory == m_kernel_page_directory.ptr());
page_directory.m_physical_pages.set(page_directory_index, move(page_table));
}
}