Hello,
I need to get the XSAVE size from userspace. The easiest way seems to be
to use the XEN_DOMCTL_getvcpuextstate hypercall, but that hypercall is
not public / there's no xenctrl.h wrapper for it.
There's also struct hvm_hw_cpu_xsave, which I can get to, but it doesn't
have a size member:
542 /*
543 * The save area of XSAVE/XRSTOR.
544 */
545
546 struct hvm_hw_cpu_xsave {
547 uint64_t xfeature_mask; /* Ignored */
548 uint64_t xcr0; /* Updated by XSETBV */
549 uint64_t xcr0_accum; /* Updated by XSETBV */
550 struct {
551 struct { char x[512]; } fpu_sse;
552
553 struct {
554 uint64_t xstate_bv; /* Updated by XRSTOR */
555 uint64_t reserved[7];
556 } xsave_hdr; /* The 64-byte header */
557
558 struct { char x[0]; } ymm; /* YMM */
559 } save_area;
560 };
I see that in the hypervisor code the length is computed by using the
HVM_CPU_XSAVE_SIZE() macro:
2126 #define HVM_CPU_XSAVE_SIZE(xcr0) (offsetof(struct hvm_hw_cpu_xsave, \
2127 save_area) + \
2128 xstate_ctxt_size(xcr0))
where:
256 static unsigned int _xstate_ctxt_size(u64 xcr0)
257 {
258 u64 act_xcr0 = get_xcr0();
259 u32 eax, ebx = 0, ecx, edx;
260 bool_t ok = set_xcr0(xcr0);
261
262 ASSERT(ok);
263 cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
264 ASSERT(ebx <= ecx);
265 ok = set_xcr0(act_xcr0);
266 ASSERT(ok);
267
268 return ebx;
269 }
270
271 /* Fastpath for common xstate size requests, avoiding reloads of
xcr0. */
272 unsigned int xstate_ctxt_size(u64 xcr0)
273 {
274 if ( xcr0 == xfeature_mask )
275 return xsave_cntxt_size;
276
277 if ( xcr0 == 0 )
278 return 0;
279
280 return _xstate_ctxt_size(xcr0);
281 }
But that doesn't seem to translate cleanly to userspace code.
I had hoped that I would be able to get this with no custom Xen patches,
is there a simpler way I'm not aware of to get to this information? And
if there isn't, would you prefer a libxc patch that exposes
XEN_DOMCTL_getvcpuextstate, or one that adds a size member to struct
hvm_hw_cpu_xsave (I'd guess the latter)?
Thanks,
Razvan
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