On 05/26/2010 09:04 PM, Glauber Costa wrote:
This patch adds a file that documents the usage of KVM-specific
MSRs.
Looks good. A few comments:
+
+Custom MSR list
+--------
+
+The current supported Custom MSR list is:
+
+MSR_KVM_WALL_CLOCK: 0x11
+
+ data: physical address of a memory area.
Which must be in guest RAM (i.e., don't point it somewhere random and
expect the hypervisor to allocate it for you).
Must be aligned to 4 bytes (we don't enforce it though).
+
+MSR_KVM_SYSTEM_TIME: 0x12
+
+ data: physical address of a memory area. This memory is expected to
+ hold a copy of the following structure:
In guest RAM. What are the alignment restrictions? I don't think we
can restrict to less than 4 bytes without breaking guests retroactively.
+
+ struct pvclock_vcpu_time_info {
+ u32 version;
+ u32 pad0;
+ u64 tsc_timestamp;
+ u64 system_time;
+ u32 tsc_to_system_mul;
+ s8 tsc_shift;
+ u8 flags;
+ u8 pad[2];
+ } __attribute__((__packed__)); /* 32 bytes */
+
+ whose data will be filled in by the hypervisor periodically. Only one
+ write, or registration, is needed for each VCPU. The interval between
+ updates of this structure is arbitrary, and implementation-dependent.
+
+ version: guest has to check version before and after grabbing
+ time information, and check that they are both equal and even.
+ An odd version indicates an in-progress update.
+
+ tsc_timestamp: the tsc value at the current VCPU, at the time
+ of the update of this structure. Guests can subtract this value
+ from current tsc to derive a notion of elapsed time since the
+ structure update.
+
+ system_time: the current system time at the time this structure
+ was last updated. Unit is nanoseconds.
What is the baseline for system_time? Guest boot?
+
+ tsc_to_system_mul: a function of the tsc frequency. One has
+ to multiply any tsc-related quantity by this value to get
+ a value in nanoseconds, besides dividing by 2^tsc_shift
+
+ tsc_shift: cycle to nanosecond divider, as a power of two, to
+ allow for shift rights. One has to shift right any tsc-related
+ quantity by this value to get a value in nanoseconds, besides
+ multiplying by tsc_to_system_mul.
Would be good to write down the formula for calculating time here.
+
+ flags: bits in this field indicate extended capabilities
+ coordinated between the guest and the hypervisor. Availability
+ of specific flags has to be checked in 0x40000001 cpuid leaf.
+ Refer to cpuid.txt for details.
Need to document bit 0 here for completeness. cpuid.txt documents how
to discover it, here we document how to use it.
+
+ Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid
+ leaf prior to usage.
+
+ This MSR falls outside the reserved KVM range, and may be removed in the
+ future. Its usage is deprecated.
+
+MSR_KVM_WALL_CLOCK_NEW: 0x4b564d00
+
+ data and functioning: same as MSR_KVM_WALL_CLOCK. Use this instead.
+
+ Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
+ leaf prior to usage.
+
+MSR_KVM_SYSTEM_TIME_NEW: 0x4b564d01
+
+ data and functioning: same as MSR_KVM_SYSTEM_TIME. Use this instead.
+
+ Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid
+ leaf prior to usage.
+
Please detail the suggested algorithm for using the msrs (new then old).
--
error compiling committee.c: too many arguments to function
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