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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCHv3 2/3] x86/fpu: Add a per-domain field to set the width of FIP/FDP
The x86 architecture allows either: a) the 64-bit FIP/FDP registers to
be restored (clearing FCS and FDS); or b) the 32-bit FIP/FDP and
FCS/FDS registers to be restored (clearing the upper 32-bits).
Add a per-domain field to indicate which of these options a guest
needs. The options are: 8, 4 or 0. Where 0 indicates that the
hypervisor should automatically guess the FIP width by checking the
value of FIP/FDP when saving the state (this is the existing
behaviour).
The FIP width is initially automatic but is set explicitly in the
following cases:
- 32-bit PV guest: 4
- Newer CPUs that do not save FCS/FDS: 8
The x87_fip_width field is placed into an existing 1 byte hole in
struct arch_domain.
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
v3:
- Skip checking for FIP updates if 8 is always requested.
- Only update word size if FP state was requested.
- Improve comments a bit.
v2:
- Retain logic to detect if XSAVE* writes FIP/FDP.
- Keep 64-bit PV guests in auto-mode.
---
xen/arch/x86/domain.c | 10 ++++++++++
xen/arch/x86/i387.c | 19 ++++++++++++-------
xen/arch/x86/xstate.c | 32 ++++++++++++++++++++------------
xen/include/asm-x86/domain.h | 15 +++++++++++++++
4 files changed, 57 insertions(+), 19 deletions(-)
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 9d43f7b..a6d721b 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -343,6 +343,8 @@ int switch_native(struct domain *d)
hvm_set_mode(v, 8);
}
+ d->arch.x87_fip_width = cpu_has_fpu_sel ? 0 : 8;
+
return 0;
}
@@ -377,6 +379,8 @@ int switch_compat(struct domain *d)
domain_set_alloc_bitsize(d);
+ d->arch.x87_fip_width = 4;
+
return 0;
undo_and_fail:
@@ -653,6 +657,12 @@ int arch_domain_create(struct domain *d, unsigned int
domcr_flags,
/* PV/PVH guests get an emulated PIT too for video BIOSes to use. */
pit_init(d, cpu_khz);
+ /*
+ * If the FPU does not save FCS/FDS then we can always
+ * save/restore the 64-bit FIP/FDP and ignore the selectors.
+ */
+ d->arch.x87_fip_width = cpu_has_fpu_sel ? 0 : 8;
+
return 0;
fail:
diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 67016c9..c29d0fa 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -144,9 +144,9 @@ static inline void fpu_xsave(struct vcpu *v)
static inline void fpu_fxsave(struct vcpu *v)
{
typeof(v->arch.xsave_area->fpu_sse) *fpu_ctxt = v->arch.fpu_ctxt;
- int word_size = cpu_has_fpu_sel ? 8 : 0;
+ unsigned int fip_width = v->domain->arch.x87_fip_width;
- if ( !is_pv_32bit_vcpu(v) )
+ if ( fip_width != 4 )
{
/*
* The only way to force fxsaveq on a wide range of gas versions.
@@ -164,7 +164,11 @@ static inline void fpu_fxsave(struct vcpu *v)
boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
return;
- if ( word_size > 0 &&
+ /*
+ * If the FIP/FDP[63:32] are both zero, it is safe to use the
+ * 32-bit restore to also restore the selectors.
+ */
+ if ( !fip_width &&
!((fpu_ctxt->fip.addr | fpu_ctxt->fdp.addr) >> 32) )
{
struct ix87_env fpu_env;
@@ -172,17 +176,18 @@ static inline void fpu_fxsave(struct vcpu *v)
asm volatile ( "fnstenv %0" : "=m" (fpu_env) );
fpu_ctxt->fip.sel = fpu_env.fcs;
fpu_ctxt->fdp.sel = fpu_env.fds;
- word_size = 4;
+ fip_width = 4;
}
+ else
+ fip_width = 8;
}
else
{
asm volatile ( "fxsave %0" : "=m" (*fpu_ctxt) );
- word_size = 4;
+ fip_width = 4;
}
- if ( word_size >= 0 )
- fpu_ctxt->x[FPU_WORD_SIZE_OFFSET] = word_size;
+ fpu_ctxt->x[FPU_WORD_SIZE_OFFSET] = fip_width;
}
/*******************************/
diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 6a917f8..fa45ad9 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -249,7 +249,7 @@ void xsave(struct vcpu *v, uint64_t mask)
struct xsave_struct *ptr = v->arch.xsave_area;
uint32_t hmask = mask >> 32;
uint32_t lmask = mask;
- int word_size = mask & XSTATE_FP ? (cpu_has_fpu_sel ? 8 : 0) : -1;
+ unsigned int fip_width = v->domain->arch.x87_fip_width;
#define XSAVE(pfx) \
alternative_io_3(".byte " pfx "0x0f,0xae,0x27\n", /* xsave */ \
".byte " pfx "0x0f,0xae,0x37\n", /* xsaveopt */ \
@@ -261,7 +261,15 @@ void xsave(struct vcpu *v, uint64_t mask)
"=m" (*ptr), \
"a" (lmask), "d" (hmask), "D" (ptr))
- if ( word_size <= 0 || !is_pv_32bit_vcpu(v) )
+ if ( fip_width == 8 )
+ {
+ XSAVE("0x48,");
+ }
+ else if ( fip_width == 4 )
+ {
+ XSAVE("");
+ }
+ else
{
uint64_t orig_fip;
static const uint64_t bad_fip = 0x6a3f5c4b13a533f6;
@@ -288,25 +296,25 @@ void xsave(struct vcpu *v, uint64_t mask)
return;
}
- if ( word_size > 0 &&
- !((ptr->fpu_sse.fip.addr | ptr->fpu_sse.fdp.addr) >> 32) )
+ /*
+ * If the FIP/FDP[63:32] are both zero, it is safe to use the
+ * 32-bit restore to also restore the selectors.
+ */
+ if ( !((ptr->fpu_sse.fip.addr | ptr->fpu_sse.fdp.addr) >> 32) )
{
struct ix87_env fpu_env;
asm volatile ( "fnstenv %0" : "=m" (fpu_env) );
ptr->fpu_sse.fip.sel = fpu_env.fcs;
ptr->fpu_sse.fdp.sel = fpu_env.fds;
- word_size = 4;
+ fip_width = 4;
}
- }
- else
- {
- XSAVE("");
- word_size = 4;
+ else
+ fip_width = 8;
}
#undef XSAVE
- if ( word_size >= 0 )
- ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] = word_size;
+ if ( mask & XSTATE_FP )
+ ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] = fip_width;
}
void xrstor(struct vcpu *v, uint64_t mask)
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 4fad638..7135709 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -339,6 +339,21 @@ struct arch_domain
u8 x86_vendor; /* CPU vendor */
u8 x86_model; /* CPU model */
+ /*
+ * The width of the FIP/FDP register in the FPU that needs to be
+ * saved/restored during a context switch. This is needed because
+ * the FPU can either: a) restore the 64-bit FIP/FDP and clear FCS
+ * and FDS; or b) restore the 32-bit FIP/FDP (clearing the upper
+ * 32-bits of FIP/FDP) and restore FCS/FDS.
+ *
+ * Which one is needed depends on the guest.
+ *
+ * This can be either: 8, 4 or 0. 0 means auto-detect the size
+ * based on the width of FIP/FDP values that are written by the
+ * guest.
+ */
+ uint8_t x87_fip_width;
+
cpuid_input_t *cpuids;
struct PITState vpit;
--
2.1.4
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