[PATCH v2 16/17] kvm: x86: Rework identity map and TSS setup for larger BIOS sizes

Jan Kiszka
2011-01-03T08:33:30Z

From: Jan Kiszka <jan.kiszka@siemens.com>

First of all, we only need this EPT identity and TSS reservation on
Intel CPUs. Then, in order to support loading BIOSes > 256K, reorder the
code, adjusting the base if the kernel supports moving the identity map.
We can drop the check for KVM_CAP_SET_TSS_ADDR as we already depend on
much newer features.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
target-i386/kvm.c | 91 ++++++++++++++++++++++++----------------------------
1 files changed, 42 insertions(+), 49 deletions(-)

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 6d31dde..caca407 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -575,23 +575,12 @@ static int kvm_get_supported_msrs(void)
return ret;
}

-static int kvm_init_identity_map_page(void)
+static bool host_supports_vmx(void)
{
-#ifdef KVM_CAP_SET_IDENTITY_MAP_ADDR
- int ret;
- uint64_t addr = 0xfffbc000;
-
- if (!kvm_check_extension(KVM_CAP_SET_IDENTITY_MAP_ADDR)) {
- return 0;
- }
+ uint32_t ecx, unused;

- ret = kvm_vm_ioctl(KVM_SET_IDENTITY_MAP_ADDR, &addr);
- if (ret < 0) {
- fprintf(stderr, "kvm_set_identity_map_addr: %s\n", strerror(ret));
- return ret;
- }
-#endif
- return 0;
+ host_cpuid(1, 0, &unused, &unused, &ecx, &unused);
+ return ecx & CPUID_EXT_VMX;
}

int kvm_arch_init(void)
@@ -611,35 +600,47 @@ int kvm_arch_init(void)
uname(&utsname);
lm_capable_kernel = strcmp(utsname.machine, "x86_64") == 0;

- /* create vm86 tss. KVM uses vm86 mode to emulate 16-bit code
- * directly. In order to use vm86 mode, a TSS is needed. Since this
- * must be part of guest physical memory, we need to allocate it. Older
- * versions of KVM just assumed that it would be at the end of physical
- * memory but that doesn't work with more than 4GB of memory. We simply
- * refuse to work with those older versions of KVM. */
- ret = kvm_check_extension(KVM_CAP_SET_TSS_ADDR);
- if (ret <= 0) {
- fprintf(stderr, "kvm does not support KVM_CAP_SET_TSS_ADDR\n");
- return ret;
- }
+ if (host_supports_vmx()) {
+ /*
+ * On older Intel CPUs, KVM uses vm86 mode to emulate 16-bit code
+ * directly. In order to use vm86 mode, an EPT identity map and a TSS
+ * are needed. Since these must be part of guest physical memory, we
+ * need to allocate them, both by setting their start addresses in the
+ * kernel and by creating a corresponding e820 entry. We need 4 pages
+ * before the BIOS.
+ *
+ * Older KVM versions may not support setting the identity map base.
+ * In that case we need to stick with the default, i.e. a 256K maximum
+ * BIOS size.
+ */
+ uint64_t identity_base = 0xfffbc000;

- /* this address is 3 pages before the bios, and the bios should present
- * as unavaible memory. FIXME, need to ensure the e820 map deals with
- * this?
- */
- /*
- * Tell fw_cfg to notify the BIOS to reserve the range.
- */
- if (e820_add_entry(0xfffbc000, 0x4000, E820_RESERVED) < 0) {
- perror("e820_add_entry() table is full");
- exit(1);
- }
- ret = kvm_vm_ioctl(KVM_SET_TSS_ADDR, 0xfffbd000);
- if (ret < 0) {
- return ret;
+#ifdef KVM_CAP_SET_IDENTITY_MAP_ADDR
+ if (kvm_check_extension(KVM_CAP_SET_IDENTITY_MAP_ADDR)) {
+ /* Allows up to 16M BIOSes. */
+ identity_base = 0xfeffc000;
+
+ ret = kvm_vm_ioctl(KVM_SET_IDENTITY_MAP_ADDR, &identity_base);
+ if (ret < 0) {
+ return ret;
+ }
+ }
+#endif
+ /* Set TSS base one page after EPT identity map. */
+ ret = kvm_vm_ioctl(KVM_SET_TSS_ADDR, identity_base + 0x1000);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* Tell fw_cfg to notify the BIOS to reserve the range. */
+ ret = e820_add_entry(identity_base, 0x4000, E820_RESERVED);
+ if (ret < 0) {
+ fprintf(stderr, "e820_add_entry() table is full\n");
+ return ret;
+ }
}

- return kvm_init_identity_map_page();
+ return 0;
}

static void set_v8086_seg(struct kvm_segment *lhs, const SegmentCache *rhs)
@@ -1592,14 +1593,6 @@ static int kvm_handle_halt(CPUState *env)
return 1;
}

-static bool host_supports_vmx(void)
-{
- uint32_t ecx, unused;
-
- host_cpuid(1, 0, &unused, &unused, &ecx, &unused);
- return ecx & CPUID_EXT_VMX;
-}
-
#define VMX_INVALID_GUEST_STATE 0x80000021

int kvm_arch_handle_exit(CPUState *env, struct kvm_run *run)
--
1.7.1