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

Browse source 
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
commit 5b7f8634e3
Notes: sideshowbarker 2024-07-19 11:26:33 +09:00
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));
}
}