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https://github.com/SerenityOS/serenity
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30861daa93
Before this change, we had File::mmap() which did all the work of setting up a VMObject, and then creating a Region in the current process's address space. This patch simplifies the interface by removing the region part. Files now only have to return a suitable VMObject from vmobject_for_mmap(), and then sys$mmap() itself will take care of actually mapping it into the address space. This fixes an issue where we'd try to block on I/O (for inode metadata lookup) while holding the address space spinlock. It also reduces time spent holding the address space lock.
69 lines
2.7 KiB
C++
69 lines
2.7 KiB
C++
/*
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* Copyright (c) 2021, Liav A. <liavalb@hotmail.co.il>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Memory.h>
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#include <AK/StdLibExtras.h>
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#include <Kernel/Devices/DeviceManagement.h>
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#include <Kernel/Devices/MemoryDevice.h>
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#include <Kernel/Memory/AnonymousVMObject.h>
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#include <Kernel/Memory/TypedMapping.h>
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#include <Kernel/Sections.h>
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namespace Kernel {
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UNMAP_AFTER_INIT NonnullLockRefPtr<MemoryDevice> MemoryDevice::must_create()
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{
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auto memory_device_or_error = DeviceManagement::try_create_device<MemoryDevice>();
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// FIXME: Find a way to propagate errors
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VERIFY(!memory_device_or_error.is_error());
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return memory_device_or_error.release_value();
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}
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UNMAP_AFTER_INIT MemoryDevice::MemoryDevice()
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: CharacterDevice(1, 1)
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{
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}
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UNMAP_AFTER_INIT MemoryDevice::~MemoryDevice() = default;
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ErrorOr<size_t> MemoryDevice::read(OpenFileDescription&, u64 offset, UserOrKernelBuffer& buffer, size_t length)
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{
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if (!MM.is_allowed_to_read_physical_memory_for_userspace(PhysicalAddress(offset), length)) {
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dbgln_if(MEMORY_DEVICE_DEBUG, "MemoryDevice: Trying to read physical memory at {} for range of {} bytes failed due to violation of access", PhysicalAddress(offset), length);
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return EINVAL;
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}
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auto mapping = TRY(Memory::map_typed<u8>(PhysicalAddress(offset), length));
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auto bytes = ReadonlyBytes { mapping.ptr(), length };
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TRY(buffer.write(bytes));
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return length;
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}
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ErrorOr<NonnullLockRefPtr<Memory::VMObject>> MemoryDevice::vmobject_for_mmap(Process&, Memory::VirtualRange const& range, u64& offset, bool)
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{
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auto viewed_address = PhysicalAddress(offset);
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// Note: This check happens to guard against possible memory leak.
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// For example, if we try to mmap physical memory from 0x1000 to 0x2000 and you
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// can actually mmap only from 0x1001, then we would fail as usual.
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// However, in such case if we mmap from 0x1002, we are technically not violating
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// any rules, besides the fact that we mapped an entire page with two bytes which we
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// were not supposed to see. To prevent that, if we use mmap(2) syscall, we should
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// always consider the start page to be aligned on PAGE_SIZE, or to be more precise
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// is to be set to the page base of that start address.
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VERIFY(viewed_address == viewed_address.page_base());
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if (!MM.is_allowed_to_read_physical_memory_for_userspace(viewed_address, range.size())) {
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dbgln_if(MEMORY_DEVICE_DEBUG, "MemoryDevice: Trying to mmap physical memory at {} for range of {} bytes failed due to violation of access", viewed_address, range.size());
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return EINVAL;
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}
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offset = 0;
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return TRY(Memory::AnonymousVMObject::try_create_for_physical_range(viewed_address, range.size()));
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}
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}
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