vmmplatsupport: support hpet emulation (#117)

Real-time Linux kernels often don't work when using the PIT. This commit adds support for emulating the HPET by adding an HPET entry to the ACPI tables. Signed-off-by: Chris Guikema <[email protected]>
seL4 · Jan 27, 2024 · 4662171 · 4662171
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diff --git a/libsel4vmmplatsupport/CMakeLists.txt b/libsel4vmmplatsupport/CMakeLists.txt
@@ -23,7 +23,18 @@ config_option(
     "KernelPlatPC99"
 )
 
+config_option(
+    LibSel4VMMUseHPET
+    VMM_USE_HPET
+    "Use the High Precision Event Timer (HPET)"
+    DEPENDS
+    "KernelX86_64VTX64BitGuests"
+    DEFAULT
+    OFF
+)
+
 mark_as_advanced(LibSel4VMMPlatsupportVESAFrameBuffer)
+mark_as_advanced(LibSel4VMMUseHPET)
 
 add_config_library(sel4vmmplatsupport "${configure_string}")
 

diff --git a/libsel4vmmplatsupport/src/arch/x86/acpi.c b/libsel4vmmplatsupport/src/arch/x86/acpi.c
@@ -19,9 +19,13 @@ Author: W.A. */
 #include <sel4vm/guest_memory_helpers.h>
 #include <platsupport/plat/acpi/acpi.h>
 
+#include <sel4vmmplatsupport/gen_config.h>
 #include <sel4vmmplatsupport/guest_memory_util.h>
 #include <sel4vmmplatsupport/arch/acpi.h>
 
+#define HPET_DEFAULT_PADDR 0xfed00000
+#define HPET_DEFAULT_TBID  0x8086a201
+
 #define APIC_FLAGS_ENABLED (1)
 
 uint8_t acpi_calc_checksum(const char *table, int length)
@@ -197,6 +201,26 @@ int make_guest_acpi_tables(vm_t *vm)
 
     // Could set up other tables here...
 
+#ifdef CONFIG_VMM_USE_HPET
+    // HPET
+    int hpet_size = sizeof(acpi_hpet_t);
+    acpi_hpet_t *hpet = calloc(1, hpet_size);
+    assert(NULL != hpet);
+
+    acpi_fill_table_head(&hpet->header, "HPET", 1);
+
+    hpet->event_timer_block_id = HPET_DEFAULT_TBID;
+    hpet->base_address.address = HPET_DEFAULT_PADDR;
+
+    hpet->header.length = hpet_size;
+    hpet->header.checksum = acpi_calc_checksum((char *)hpet, hpet_size);
+
+    tables[num_tables] = hpet;
+    table_sizes[num_tables] = hpet_size;
+
+    num_tables++;
+#endif
+
     // DSDT
     int dsdt_size = sizeof(acpi_dsdt_t);
     acpi_dsdt_t *dsdt = calloc(1, dsdt_size);