From 7212bc6c8e9b4a3118e1cc90157c2f123198139e Mon Sep 17 00:00:00 2001 From: Gerd Hoffmann Date: Thu, 16 Jan 2014 10:25:57 +0100 Subject: [PATCH 02/14] pc_piix: document gigabyte_align RH-Author: Gerd Hoffmann Message-id: <1389867959-12463-3-git-send-email-kraxel@redhat.com> Patchwork-id: 56745 O-Subject: [RHEL-7 qemu-kvm PATCH 2/4] pc_piix: document gigabyte_align Bugzilla: 1026548 RH-Acked-by: Laszlo Ersek RH-Acked-by: Igor Mammedov RH-Acked-by: Paolo Bonzini From: "Michael S. Tsirkin" Document the logic behind the below/above 4G split. Signed-off-by: Michael S. Tsirkin (cherry picked from commit ecdbfceb0f20a3ef784bf522ed7264660aa3d150) Conflicts: hw/i386/pc_piix.c --- hw/i386/pc_piix.c | 11 +++++++++++ 1 file changed, 11 insertions(+) Signed-off-by: Miroslav Rezanina --- hw/i386/pc_piix.c | 11 +++++++++++ 1 files changed, 11 insertions(+), 0 deletions(-) diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c index 9f1d0b5..12351f9 100644 --- a/hw/i386/pc_piix.c +++ b/hw/i386/pc_piix.c @@ -61,6 +61,10 @@ static const int ide_irq[MAX_IDE_BUS] = { 14, 15 }; static bool smbios_type1_defaults = true; static bool has_pci_info; static bool has_acpi_build = true; +/* Make sure that guest addresses aligned at 1Gbyte boundaries get mapped to + * host addresses aligned at 1Gbyte boundaries. This way we can use 1GByte + * pages in the host. + */ static bool gigabyte_align = true; /* PC hardware initialisation */ @@ -102,6 +106,13 @@ static void pc_init1(QEMUMachineInitArgs *args, kvmclock_create(); } + /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory). + * If it doesn't, we need to split it in chunks below and above 4G. + * In any case, try to make sure that guest addresses aligned at + * 1G boundaries get mapped to host addresses aligned at 1G boundaries. + * For old machine types, use whatever split we used historically to avoid + * breaking migration. + */ if (args->ram_size >= 0xe0000000) { ram_addr_t lowmem = gigabyte_align ? 0xc0000000 : 0xe0000000; above_4g_mem_size = args->ram_size - lowmem; -- 1.7.1