[kernel] Set framebuffer to write-combining

Several changes were needed to make this work:

- Update the page_table::flags to understand memory caching types
- Set up the PAT MSR to add the WC option
- Make page-offset area mapped as WT
- Add all the MTRR and PAT MSRs, and log the MTRRs for verification
- Add a vm_area flag for write_combining

src/kernel/msr.h

@@ -6,22 +6,46 @@
 
 enum class msr : uint32_t
 {
-	ia32_efer			= 0xc0000080,
-	ia32_star			= 0xc0000081,
-	ia32_lstar			= 0xc0000082,
-	ia32_fmask			= 0xc0000084,
+	ia32_mtrrcap           = 0x000000fe,
+	ia32_mtrrdeftype       = 0x000002ff,
 
-	ia32_gs_base		= 0xc0000101,
-	ia32_kernel_gs_base = 0xc0000102
+	ia32_mtrrphysbase      = 0x00000200,
+	ia32_mtrrphysmask      = 0x00000201,
+
+	ia32_mtrrfix64k_00000  = 0x00000250,
+
+	ia32_mtrrfix16k_80000  = 0x00000258,
+	ia32_mtrrfix16k_a0000  = 0x00000259,
+
+	ia32_mtrrfix4k_c0000   = 0x00000268,
+	ia32_mtrrfix4k_c8000   = 0x00000269,
+	ia32_mtrrfix4k_d0000   = 0x0000026A,
+	ia32_mtrrfix4k_d8000   = 0x0000026B,
+	ia32_mtrrfix4k_e0000   = 0x0000026C,
+	ia32_mtrrfix4k_e8000   = 0x0000026D,
+	ia32_mtrrfix4k_f0000   = 0x0000026E,
+	ia32_mtrrfix4k_f8000   = 0x0000026F,
+
+	ia32_pat               = 0x00000277,
+	ia32_efer              = 0xc0000080,
+	ia32_star              = 0xc0000081,
+	ia32_lstar             = 0xc0000082,
+	ia32_fmask             = 0xc0000084,
+
+	ia32_gs_base           = 0xc0000101,
+	ia32_kernel_gs_base    = 0xc0000102
 };
 
+/// Find the msr for MTRR physical base or mask
+msr find_mtrr(msr type, unsigned index);
+
 /// Read the value of a MSR
-/// \arg addr   The MSR address
-/// \returns    The current value of the MSR
+/// \arg addr  The MSR address
+/// \returns   The current value of the MSR
 uint64_t rdmsr(msr addr);
 
 /// Write to a MSR
-/// \arg addr   The MSR address
-/// \arg value  The value to write
+/// \arg addr  The MSR address
+/// \arg value The value to write
 void wrmsr(msr addr, uint64_t value);