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Revert "Kernel: Avoid a memcpy() of the whole block when paging in from inode"

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This reverts commit 11896d0e26.

This caused a race where other processes using the same InodeVMObject
could end up accessing the newly-mapped physical page before we've
actually filled it with bytes from disk.

It would be nice to avoid these copies without breaking anything.
This commit is contained in:
Andreas Kling 2019-08-26 13:47:17 +02:00
parent f5d779f47e
commit dde10f534f
Notes: sideshowbarker 2024-07-19 12:30:36 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/dde10f534f5
1 changed files with 17 additions and 14 deletions
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31
Kernel/VM/MemoryManager.cpp
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@ -342,14 +342,14 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
ASSERT(vmo.is_inode());
auto& inode_vmobject = static_cast<InodeVMObject&>(vmo);
auto& vmo_page = inode_vmobject.physical_pages()[region.first_page_index() + page_index_in_region];
InterruptFlagSaver saver;
bool interrupts_were_enabled = are_interrupts_enabled();
if (!interrupts_were_enabled)
sti();
sti();
LOCKER(vmo.m_paging_lock);
cli();
if (!vmo_page.is_null()) {
#ifdef PAGE_FAULT_DEBUG
@ -362,6 +362,19 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
#ifdef MM_DEBUG
dbgprintf("MM: page_in_from_inode ready to read from inode\n");
#endif
sti();
u8 page_buffer[PAGE_SIZE];
auto& inode = inode_vmobject.inode();
auto nread = inode.read_bytes((region.first_page_index() + page_index_in_region) * PAGE_SIZE, PAGE_SIZE, page_buffer, nullptr);
if (nread < 0) {
kprintf("MM: page_in_from_inode had error (%d) while reading!\n", nread);
return false;
}
if (nread < PAGE_SIZE) {
// If we read less than a page, zero out the rest to avoid leaking uninitialized data.
memset(page_buffer + nread, 0, PAGE_SIZE - nread);
}
cli();
vmo_page = allocate_user_physical_page(ShouldZeroFill::No);
if (vmo_page.is_null()) {
kprintf("MM: page_in_from_inode was unable to allocate a physical page\n");
@ -369,17 +382,7 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
}
remap_region_page(region, page_index_in_region);
u8* dest_ptr = region.vaddr().offset(page_index_in_region * PAGE_SIZE).as_ptr();
auto& inode = inode_vmobject.inode();
auto nread = inode.read_bytes((region.first_page_index() + page_index_in_region) * PAGE_SIZE, PAGE_SIZE, dest_ptr, nullptr);
if (nread < 0) {
kprintf("MM: page_in_from_inode had error (%d) while reading!\n", nread);
return false;
}
if (nread < PAGE_SIZE) {
// If we read less than a page, zero out the rest to avoid leaking uninitialized data.
memset(dest_ptr + nread, 0, PAGE_SIZE - nread);
}
memcpy(dest_ptr, page_buffer, PAGE_SIZE);
return true;
}