Kernel: Move Kernel mapping to 0xc0000000

The kernel is now no longer identity mapped to the bottom 8MiB of
memory, and is now mapped at the higher address of `0xc0000000`.

The lower ~1MiB of memory (from GRUB's mmap), however is still
identity mapped to provide an easy way for the kernel to get
physical pages for things such as DMA etc. These could later be
mapped to the higher address too, as I'm not too sure how to
go about doing this elegantly without a lot of address subtractions.

2 files changed, 14 insertions, 10 deletions

diff --git a/Kernel/Devices/PATAChannel.cpp b/Kernel/Devices/PATAChannel.cpp
index 5e2fb84cb2..0cde8e7c9d 100644
--- a/Kernel/Devices/PATAChannel.cpp
+++ b/Kernel/Devices/PATAChannel.cpp
@@ -116,11 +116,13 @@ void PATAChannel::initialize(bool force_pio)
             kprintf("PATAChannel: PATA Controller found! id=%w:%w\n", id.vendor_id, id.device_id);
         }
     });
+
+    m_prdt_page = MM.allocate_supervisor_physical_page();
     m_force_pio.resource() = false;
     if (!m_pci_address.is_null()) {
         // Let's try to set up DMA transfers.
         PCI::enable_bus_mastering(m_pci_address);
-        m_prdt.end_of_table = 0x8000;
+        prdt().end_of_table = 0x8000;
         m_bus_master_base = PCI::get_BAR4(m_pci_address) & 0xfffc;
         m_dma_buffer_page = MM.allocate_supervisor_physical_page();
         kprintf("PATAChannel: Bus master IDE: I/O @ %x\n", m_bus_master_base);
@@ -259,16 +261,16 @@ bool PATAChannel::ata_read_sectors_with_dma(u32 lba, u16 count, u8* outbuf, bool
 
     disable_irq();
 
-    m_prdt.offset = m_dma_buffer_page->paddr();
-    m_prdt.size = 512 * count;
+    prdt().offset = m_dma_buffer_page->paddr();
+    prdt().size = 512 * count;
 
-    ASSERT(m_prdt.size <= PAGE_SIZE);
+    ASSERT(prdt().size <= PAGE_SIZE);
 
     // Stop bus master
     IO::out8(m_bus_master_base, 0);
 
     // Write the PRDT location
-    IO::out32(m_bus_master_base + 4, (u32)&m_prdt);
+    IO::out32(m_bus_master_base + 4, (u32)&prdt());
 
     // Turn on "Interrupt" and "Error" flag. The error flag should be cleared by hardware.
     IO::out8(m_bus_master_base + 2, IO::in8(m_bus_master_base + 2) | 0x6);
@@ -338,18 +340,18 @@ bool PATAChannel::ata_write_sectors_with_dma(u32 lba, u16 count, const u8* inbuf
 
     disable_irq();
 
-    m_prdt.offset = m_dma_buffer_page->paddr();
-    m_prdt.size = 512 * count;
+    prdt().offset = m_dma_buffer_page->paddr();
+    prdt().size = 512 * count;
 
     memcpy(m_dma_buffer_page->paddr().as_ptr(), inbuf, 512 * count);
 
-    ASSERT(m_prdt.size <= PAGE_SIZE);
+    ASSERT(prdt().size <= PAGE_SIZE);
 
     // Stop bus master
     IO::out8(m_bus_master_base, 0);
 
     // Write the PRDT location
-    IO::out32(m_bus_master_base + 4, (u32)&m_prdt);
+    IO::out32(m_bus_master_base + 4, (u32)&prdt());
 
     // Turn on "Interrupt" and "Error" flag. The error flag should be cleared by hardware.
     IO::out8(m_bus_master_base + 2, IO::in8(m_bus_master_base + 2) | 0x6);
diff --git a/Kernel/Devices/PATAChannel.h b/Kernel/Devices/PATAChannel.h
index 0806c2fa8c..7a1a4ca1a0 100644
--- a/Kernel/Devices/PATAChannel.h
+++ b/Kernel/Devices/PATAChannel.h
@@ -55,6 +55,8 @@ private:
     bool ata_read_sectors(u32, u16, u8*, bool);
     bool ata_write_sectors(u32, u16, const u8*, bool);
 
+    PhysicalRegionDescriptor& prdt() { return *reinterpret_cast<PhysicalRegionDescriptor*>(m_prdt_page->paddr().as_ptr()); }
+
     // Data members
     u8 m_channel_number { 0 }; // Channel number. 0 = master, 1 = slave
     u16 m_io_base { 0x1F0 };
@@ -63,7 +65,7 @@ private:
     volatile bool m_interrupted { false };
 
     PCI::Address m_pci_address;
-    PhysicalRegionDescriptor m_prdt;
+    RefPtr<PhysicalPage> m_prdt_page;
     RefPtr<PhysicalPage> m_dma_buffer_page;
     u16 m_bus_master_base { 0 };
     Lockable<bool> m_dma_enabled;