47 lines
2.0 KiB
Diff
47 lines
2.0 KiB
Diff
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# HG changeset patch
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# User Jan Beulich <jbeulich@suse.com>
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# Date 1358341015 -3600
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# Node ID b4cbb83f9a1f57b4f26f2d35998cda42b904ea69
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# Parent 327b812026fe62a990f1d81041729c42196983ca
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x86: consistently mask floating point exceptions
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c/s 23142:f5e8d152a565 resulted in v->arch.fpu_ctxt to point into the
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save area allocated for xsave/xrstor (when they're available). The way
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vcpu_restore_fpu_lazy() works (using fpu_init() for an uninitialized
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vCPU only when there's no xsave support) causes this to load whatever
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arch_set_info_guest() put there, irrespective of whether the i387 state
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was specified to be valid in the respective input structure.
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Consequently, with a cleared (al zeroes) incoming FPU context, and with
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xsave available, one gets all exceptions unmasked (as opposed to to the
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legacy case, where FINIT and LDMXCSR get used, masking all exceptions).
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This causes e.g. para-virtualized NetWare to crash.
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The behavior of arch_set_info_guest() is thus being made more hardware-
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like for the FPU portion of it: Considering it to be similar to INIT,
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it will leave untouched all floating point state now. An alternative
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would be to make the behavior RESET-like, forcing all state to known
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values, albeit - taking into account legacy behavior - not to precisely
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the values RESET would enforce (which masks only SSE exceptions, but
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not x87 ones); that would come closest to mimicing FINIT behavior in
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the xsave case. Another option would be to continue copying whatever
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was provided, but override (at least) FCW and MXCSR if VGCF_I387_VALID
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isn't set.
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Acked-by: Keir Fraser <keir@xen.org>
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--- a/xen/arch/x86/domain.c
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+++ b/xen/arch/x86/domain.c
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@@ -819,7 +819,9 @@ int arch_set_info_guest(
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v->arch.vgc_flags = flags;
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- memcpy(v->arch.fpu_ctxt, &c.nat->fpu_ctxt, sizeof(c.nat->fpu_ctxt));
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+ if ( flags & VGCF_I387_VALID )
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+ memcpy(v->arch.fpu_ctxt, &c.nat->fpu_ctxt, sizeof(c.nat->fpu_ctxt));
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+
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if ( !compat )
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{
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memcpy(&v->arch.user_regs, &c.nat->user_regs, sizeof(c.nat->user_regs));
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