Date: Sun, 17 May 2020 11:09:38 +0000 (UTC) From: Peter Grehan <grehan@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r361131 - stable/12/sys/amd64/vmm Message-ID: <202005171109.04HB9ckh023048@repo.freebsd.org>
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Author: grehan Date: Sun May 17 11:09:38 2020 New Revision: 361131 URL: https://svnweb.freebsd.org/changeset/base/361131 Log: MFC r361064 Hide host CPUID 0x15 TSC/Crystal ratio/freq info from guest In recent Linux (5.3+) and OpenBSD (6.6+) kernels, and with hosts that support CPUID 0x15, the local APIC frequency is determined directly from the reported crystal clock to avoid calibration against the 8254 timer. However, the local APIC frequency implemented by bhyve is 128MHz, where most h/w systems report frequencies around 25MHz. This shows up on OpenBSD guests as repeated keystrokes on the emulated PS2 keyboard when using VNC, since the kernel's timers are now much shorter. Fix by reporting all-zeroes for CPUID 0x15. This allows guests to fall back to using the 8254 to calibrate the local APIC frequency. Future work could be to compute values returned for 0x15 that would match the host TSC and bhyve local APIC frequency, though all dependencies on this would need to be examined (for example, Linux will start using 0x16 for some hosts). PR: 246321 Reported by: Jason Tubnor (and tested) Approved by: bz (mentor) Modified: stable/12/sys/amd64/vmm/x86.c stable/12/sys/amd64/vmm/x86.h Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/amd64/vmm/x86.c ============================================================================== --- stable/12/sys/amd64/vmm/x86.c Sun May 17 09:34:29 2020 (r361130) +++ stable/12/sys/amd64/vmm/x86.c Sun May 17 11:09:38 2020 (r361131) @@ -559,6 +559,18 @@ x86_emulate_cpuid(struct vm *vm, int vcpu_id, } break; + case CPUID_0000_0015: + /* + * Don't report CPU TSC/Crystal ratio and clock + * values since guests may use these to derive the + * local APIC frequency.. + */ + regs[0] = 0; + regs[1] = 0; + regs[2] = 0; + regs[3] = 0; + break; + case 0x40000000: regs[0] = CPUID_VM_HIGH; bcopy(bhyve_id, ®s[1], 4); Modified: stable/12/sys/amd64/vmm/x86.h ============================================================================== --- stable/12/sys/amd64/vmm/x86.h Sun May 17 09:34:29 2020 (r361130) +++ stable/12/sys/amd64/vmm/x86.h Sun May 17 11:09:38 2020 (r361131) @@ -41,6 +41,7 @@ #define CPUID_0000_000A (0xA) #define CPUID_0000_000B (0xB) #define CPUID_0000_000D (0xD) +#define CPUID_0000_0015 (0x15) #define CPUID_8000_0000 (0x80000000) #define CPUID_8000_0001 (0x80000001) #define CPUID_8000_0002 (0x80000002)
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