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With CPUID features suitably masked this is supposed to work, but was
completely broken (i.e. the case wasn't even considered when the
original xsave save/restore code was written).
First of all, xsave_enabled() wrongly returned the value of
cpu_has_xsave, i.e. not even taking into consideration attributes of
the vCPU in question. Instead this function ought to check whether the
guest ever enabled xsave support (by writing a [non-zero] value to
XCR0). As a result of this, a vCPU's xcr0 and xcr0_accum must no longer
be initialized to XSTATE_FP_SSE (since that's a valid value a guest
could write to XCR0), and the xsave/xrstor as well as the context
switch code need to suitably account for this (by always enforcing at
least this part of the state to be saved/loaded).
This involves undoing large parts of c/s 22945:13a7d1f7f62c ("x86: add
strictly sanity check for XSAVE/XRSTOR") - we need to cleanly
distinguish between hardware capabilities and vCPU used features.
Next both HVM and PV save code needed tweaking to not always save the
full state supported by the underlying hardware, but just the parts
that the guest actually used. Similarly the restore code should bail
not just on state being restored that the hardware cannot handle, but
also on inconsistent save state (inconsistent XCR0 settings or size of
saved state not in line with XCR0).
And finally the PV extended context get/set code needs to use slightly
different logic than the HVM one, as here we can't just key off of
xsave_enabled() (i.e. avoid doing anything if a guest doesn't use
xsave) because the tools use this function to determine host
capabilities as well as read/write vCPU state. The set operation in
particular needs to be capable of cleanly dealing with input that
consists of only the xcr0 and xcr0_accum values (if they're both zero
then no further data is required).
While for things to work correctly both sides (saving _and_ restoring
host) need to run with the fixed code, afaict no breakage should occur
if either side isn't up to date (other than the breakage that this
patch attempts to fix).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Yang Zhang <yang.z.zhang@intel.com>
Acked-by: Keir Fraser <keir@xen.org>
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- properly validate available feature set on APs
- also validate xsaveopt availability on APs
- properly indicate whether the initialization is on the BSP (we
shouldn't be using "cpu == 0" checks for this)
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
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The initial state for a vCPU is using default values, so there's no
need to force the XRSTOR to read the state from memory. This saves a
couple of thousand restores from memory just during boot of Linux on
my Sandy Bridge system (I didn't try to make further measurements).
The above requires that arch_set_info_guest() updates the state flags
in the save area when valid floating point state got passed in, but
that would really have been needed even before in case XSAVE{,OPT}
decided to clear one or both of the FP and SSE bits.
Furthermore, hvm_vcpu_reset_state() shouldn't just clear out the FPU/
SSE area, but needs to re-initialized MXCSR and FCW.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
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- both VMX and SVM ignored the ECX input to XSETBV
- both SVM and VMX used the full 64-bit RAX when calculating the input
mask to XSETBV
- faults on XSETBV did not get recovered from
Also consolidate the handling for PV and HVM into a single function,
and make the per-CPU variable "xcr0" static to xstate.c.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
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Doing {,F}X{SAVE,RSTOR} unconditionally with 64-bit operand size leads
to the selector values associated with the last instruction/data
pointers getting lost. This, besides being inconsistent and not
compatible with native hardware behavior especially for 32-bit guests,
leads to bug checks in 32-bit Windows when running with "Driver
verifier" (see e.g. http://support.microsoft.com/kb/244617).
In a first try I made the code figure out the current guest mode, but
that has the disadvantage of only taking care of the issue when the
guest executes in the mode for which the state currently is (i.e.
namely not in the case of a 64-bit guest running a 32-bit application,
but being in kernle [64-bit] mode).
The solution presented here is to conditionally execute an auxiliary
FNSTENV and use the selectors from there.
In either case the determined word size gets stored in the last byte
of the FPU/SSE save area, which is available for software use (and I
verified is being cleared to zero by all versions of Xen, i.e. will not
present a problem when migrating guests from older to newer hosts), and
evaluated for determining the operand size {,F}XRSTOR is to be issued
with.
Note that I did check whether using a second FXSAVE or a partial second
XSAVE would be faster than FNSTENV - neither on my Westmere (FXSAVE)
nor on my Romley (XSAVE) they are.
I was really tempted to use branches into the middle of instructions
(i.e. past the REX64 prefixes) here, as that would have allowed to
collapse the otherwise identical fault recovery blocks. I stayed away
from doing so just because I expect others to dislike such slightly
subtle/tricky code.
Reported-by: Ben Guthro <Benjamin.Guthro@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
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Signed-off-by: Keir Fraser <keir@xen.org>
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Without the use of xsave, guests get their initial floating point
environment set up with finit. At least NetWare actually depends on
this (in particular on all exceptions being masked), so to be
consistent set the same environment also when using xsave. This is
also in line with all SSE exceptions getting masked initially.
To avoid further fragile casts in xstate_alloc_save_area() the patch
also changes xsave_struct's fpu_see member to have actually usable
fields.
The patch was tested in its technically identical, but modified-file-
wise different 4.1.2 version.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Charles Arnold <carnold@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
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Xen currently sets mask bits of xsave() and xrstor() to all 1's. This
patch adds a mask option to xsave() and xrstor().
Signed-off-by: Wei Huang <wei.huang2@amd.com>
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Current extended code is mixing with FPU code in i387.c. As part of
FPU code cleanup, this patch moves all extended state code into
independent files. Not much semantic are changed and most function
names are kept untouched, except for xsave() and xsaveopt(). These two
functions are combined into a single function.
Signed-off-by: Wei Huang <wei.huang2@amd.com>
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