Bug 871265
| Summary: | lahf_lm flag is not recognized by guest kernel | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 6 | Reporter: | Suqin Huang <shuang> |
| Component: | qemu-kvm | Assignee: | Eduardo Habkost <ehabkost> |
| Status: | CLOSED WONTFIX | QA Contact: | Virtualization Bugs <virt-bugs> |
| Severity: | unspecified | Docs Contact: | |
| Priority: | unspecified | ||
| Version: | 6.4 | CC: | acathrow, areis, bsarathy, dyasny, mkenneth, virt-maint |
| Target Milestone: | rc | ||
| Target Release: | --- | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Known Issue | |
| Doc Text: |
AMD Opteron G1, G2 or G3 CPU models on qemu-kvm use the family and models values as follows: family=15 and model=6. If these values are larger than 20, the lahfm_lm CPU feature is ignored by Linux guests, even when the feature is enabled. To work around this problem, use a different CPU model, for example AMD Opteron G4.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | 2012-11-20 13:47:28 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
The bit is set on the CPUID info:
eax in: 0x80000001, eax = 00000f61 ebx = 00000000 ecx = 000000e1 edx = 2193fbfd
(it's bit 0 on CPUID[0x80000001].ECX)
The guest chooses to ignore it because of the low model value. This is the guest-side kernel code:
/* On C+ stepping K8 rep microcode works well for copy/memset */
if (c->x86 == 0xf) {
u32 level;
level = cpuid_eax(1);
if ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
set_cpu_cap(c, X86_FEATURE_REP_GOOD);
/*
* Some BIOSes incorrectly force this feature, but only K8
* revision D (model = 0x14) and later actually support it.
* (AMD Erratum #110, docId: 25759).
*/
if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM)) {
u64 val;
clear_cpu_cap(c, X86_FEATURE_LAHF_LM);
if (!rdmsrl_amd_safe(0xc001100d, &val)) {
val &= ~(1ULL << 32);
wrmsrl_amd_safe(0xc001100d, val);
}
}
}
The only way to fix it would be to update the Opteron_G* models to use a higher family/model value instead of family=15,model=6.
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Description of problem: same kernel for host and guest, lahf_lm is shown on host /proc/cpuinfo but is not shown on guest /proc/cpuinfo lahf_lm cpuid is enabled from guest x86info Version-Release number of selected component (if applicable): qemu-kvm-0.12.1.2-2.329.el6.x86_64 2.6.32-337.el6.x86_64 How reproducible: 100% Steps to Reproduce: 1. boot guest with Opteron_G3 on Opteron_G3 host 2. 3. Actual results: Expected results: Additional info: 1. guest flag: (no lahf_lm) flags : fpu de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good extd_apicid unfair_spinlock pni cx16 x2apic popcnt hypervisor abm sse4a misalignsse 2. host flag: (there is lahf_lm) flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs npt lbrv svm_lock 3. lahf_lm is definded in cpuid.c static const char *ext3_feature_name[] = { "lahf_lm" /* AMD LahfSahf */, "cmp_legacy", "svm", "extapic" /* AMD ExtApicSpace */, "cr8legacy" /* AMD AltMovCr8 */, "abm", "sse4a", "misalignsse", "3dnowprefetch", "osvw", "ibs", "xop", "skinit", "wdt", NULL, NULL, "fma4", NULL, "cvt16", "nodeid_msr", 4. guest x86info eax in: 0x00000000, eax = 00000005 ebx = 68747541 ecx = 444d4163 edx = 69746e65 eax in: 0x00000001, eax = 00000f61 ebx = 01000800 ecx = 80a02001 edx = 078bf3fd eax in: 0x00000002, eax = 00000001 ebx = 00000000 ecx = 00000000 edx = 002c307d eax in: 0x00000003, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000 eax in: 0x00000004, eax = 00000121 ebx = 01c0003f ecx = 0000003f edx = 00000001 eax in: 0x00000005, eax = 00000000 ebx = 00000000 ecx = 00000003 edx = 00000000 eax in: 0x80000000, eax = 80000008 ebx = 68747541 ecx = 444d4163 edx = 69746e65 eax in: 0x80000001, eax = 00000f61 ebx = 00000000 ecx = 000000e1 edx = 2193fbfd eax in: 0x80000002, eax = 20444d41 ebx = 6574704f ecx = 206e6f72 edx = 78783332 eax in: 0x80000003, eax = 65472820 ebx = 2033206e ecx = 73616c43 edx = 704f2073 eax in: 0x80000004, eax = 6f726574 ebx = 0000296e ecx = 00000000 edx = 00000000 eax in: 0x80000005, eax = 01ff01ff ebx = 01ff01ff ecx = 40020140 edx = 40020140 eax in: 0x80000006, eax = 00000000 ebx = 42004200 ecx = 02008140 edx = 00000000 eax in: 0x80000007, eax = 00000000 ebx = 00000000 ecx = 00000000 edx = 00000000 eax in: 0x80000008, eax = 00003030 ebx = 00000000 ecx = 00000000 edx = 00000000 5. guest & host kernel 2.6.32-337.el6.x86_64