| Message ID | 20240523111627.28896-3-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | x86/xstate: Fixes to size calculations | expand |
On 23.05.2024 13:16, Andrew Cooper wrote: > Right now, xstate_ctxt_size() performs a cross-check of size with CPUID in for > every call. This is expensive, being used for domain create/migrate, as well > as to service certain guest CPUID instructions. > > Instead, arrange to check the sizes once at boot. See the code comments for > details. Right now, it just checks hardware against the algorithm > expectations. Later patches will add further cross-checking. > > Introduce the missing X86_XCR0_* and X86_XSS_* constants, and a couple of > missing CPUID bits. This is to maximise coverage in the sanity check, even if > we don't expect to use/virtualise some of these features any time soon. Leave > HDC and HWP alone for now. We don't have CPUID bits from them stored nicely. Since you say "the missing", ... > --- a/xen/arch/x86/include/asm/x86-defns.h > +++ b/xen/arch/x86/include/asm/x86-defns.h > @@ -77,7 +77,7 @@ > #define X86_CR4_PKS 0x01000000 /* Protection Key Supervisor */ > > /* > - * XSTATE component flags in XCR0 > + * XSTATE component flags in XCR0 | MSR_XSS > */ > #define X86_XCR0_FP_POS 0 > #define X86_XCR0_FP (1ULL << X86_XCR0_FP_POS) > @@ -95,11 +95,34 @@ > #define X86_XCR0_ZMM (1ULL << X86_XCR0_ZMM_POS) > #define X86_XCR0_HI_ZMM_POS 7 > #define X86_XCR0_HI_ZMM (1ULL << X86_XCR0_HI_ZMM_POS) > +#define X86_XSS_PROC_TRACE (_AC(1, ULL) << 8) > #define X86_XCR0_PKRU_POS 9 > #define X86_XCR0_PKRU (1ULL << X86_XCR0_PKRU_POS) > +#define X86_XSS_PASID (_AC(1, ULL) << 10) > +#define X86_XSS_CET_U (_AC(1, ULL) << 11) > +#define X86_XSS_CET_S (_AC(1, ULL) << 12) > +#define X86_XSS_HDC (_AC(1, ULL) << 13) > +#define X86_XSS_UINTR (_AC(1, ULL) << 14) > +#define X86_XSS_LBR (_AC(1, ULL) << 15) > +#define X86_XSS_HWP (_AC(1, ULL) << 16) > +#define X86_XCR0_TILE_CFG (_AC(1, ULL) << 17) > +#define X86_XCR0_TILE_DATA (_AC(1, ULL) << 18) ... I'm wondering if you deliberately left out APX (bit 19). Since you're re-doing some of what I have long had in patches already, I'd also like to ask whether the last underscores each in the two AMX names really are useful in your opinion. While rebasing isn't going to be difficult either way, it would be yet simpler with X86_XCR0_TILECFG and X86_XCR0_TILEDATA, as I've had it in my patches for over 3 years. > --- a/xen/arch/x86/xstate.c > +++ b/xen/arch/x86/xstate.c > @@ -604,9 +604,156 @@ static bool valid_xcr0(uint64_t xcr0) > if ( !(xcr0 & X86_XCR0_BNDREGS) != !(xcr0 & X86_XCR0_BNDCSR) ) > return false; > > + /* TILE_CFG and TILE_DATA must be the same. */ > + if ( !(xcr0 & X86_XCR0_TILE_CFG) != !(xcr0 & X86_XCR0_TILE_DATA) ) > + return false; > + > return true; > } > > +struct xcheck_state { > + uint64_t states; > + uint32_t uncomp_size; > + uint32_t comp_size; > +}; > + > +static void __init check_new_xstate(struct xcheck_state *s, uint64_t new) > +{ > + uint32_t hw_size; > + > + BUILD_BUG_ON(X86_XCR0_STATES & X86_XSS_STATES); > + > + BUG_ON(s->states & new); /* States only increase. */ > + BUG_ON(!valid_xcr0(s->states | new)); /* Xen thinks it's a good value. */ > + BUG_ON(new & ~(X86_XCR0_STATES | X86_XSS_STATES)); /* Known state. */ > + BUG_ON((new & X86_XCR0_STATES) && > + (new & X86_XSS_STATES)); /* User or supervisor, not both. */ > + > + s->states |= new; > + if ( new & X86_XCR0_STATES ) > + { > + if ( !set_xcr0(s->states & X86_XCR0_STATES) ) > + BUG(); > + } > + else > + set_msr_xss(s->states & X86_XSS_STATES); > + > + /* > + * Check the uncompressed size. Some XSTATEs are out-of-order and fill in > + * prior holes in the state area, so we check that the size doesn't > + * decrease. > + */ > + hw_size = cpuid_count_ebx(0xd, 0); > + > + if ( hw_size < s->uncomp_size ) > + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, uncompressed hw size %#x < prev size %#x\n", > + s->states, &new, hw_size, s->uncomp_size); > + > + s->uncomp_size = hw_size; > + > + /* > + * Check the compressed size, if available. All components strictly > + * appear in index order. In principle there are no holes, but some > + * components have their base address 64-byte aligned for efficiency > + * reasons (e.g. AMX-TILE) and there are other components small enough to > + * fit in the gap (e.g. PKRU) without increasing the overall length. > + */ > + hw_size = cpuid_count_ebx(0xd, 1); > + > + if ( cpu_has_xsavec ) > + { > + if ( hw_size < s->comp_size ) > + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, compressed hw size %#x < prev size %#x\n", > + s->states, &new, hw_size, s->comp_size); > + > + s->comp_size = hw_size; > + } > + else > + BUG_ON(hw_size); /* Compressed size reported, but no XSAVEC ? */ I'm not quite happy with this being fatal to booting. Maybe just WARN_ON()? Jan
On 23/05/2024 4:34 pm, Jan Beulich wrote: > On 23.05.2024 13:16, Andrew Cooper wrote: >> Right now, xstate_ctxt_size() performs a cross-check of size with CPUID in for >> every call. This is expensive, being used for domain create/migrate, as well >> as to service certain guest CPUID instructions. >> >> Instead, arrange to check the sizes once at boot. See the code comments for >> details. Right now, it just checks hardware against the algorithm >> expectations. Later patches will add further cross-checking. >> >> Introduce the missing X86_XCR0_* and X86_XSS_* constants, and a couple of >> missing CPUID bits. This is to maximise coverage in the sanity check, even if >> we don't expect to use/virtualise some of these features any time soon. Leave >> HDC and HWP alone for now. We don't have CPUID bits from them stored nicely. > Since you say "the missing", ... > >> --- a/xen/arch/x86/include/asm/x86-defns.h >> +++ b/xen/arch/x86/include/asm/x86-defns.h >> @@ -77,7 +77,7 @@ >> #define X86_CR4_PKS 0x01000000 /* Protection Key Supervisor */ >> >> /* >> - * XSTATE component flags in XCR0 >> + * XSTATE component flags in XCR0 | MSR_XSS >> */ >> #define X86_XCR0_FP_POS 0 >> #define X86_XCR0_FP (1ULL << X86_XCR0_FP_POS) >> @@ -95,11 +95,34 @@ >> #define X86_XCR0_ZMM (1ULL << X86_XCR0_ZMM_POS) >> #define X86_XCR0_HI_ZMM_POS 7 >> #define X86_XCR0_HI_ZMM (1ULL << X86_XCR0_HI_ZMM_POS) >> +#define X86_XSS_PROC_TRACE (_AC(1, ULL) << 8) >> #define X86_XCR0_PKRU_POS 9 >> #define X86_XCR0_PKRU (1ULL << X86_XCR0_PKRU_POS) >> +#define X86_XSS_PASID (_AC(1, ULL) << 10) >> +#define X86_XSS_CET_U (_AC(1, ULL) << 11) >> +#define X86_XSS_CET_S (_AC(1, ULL) << 12) >> +#define X86_XSS_HDC (_AC(1, ULL) << 13) >> +#define X86_XSS_UINTR (_AC(1, ULL) << 14) >> +#define X86_XSS_LBR (_AC(1, ULL) << 15) >> +#define X86_XSS_HWP (_AC(1, ULL) << 16) >> +#define X86_XCR0_TILE_CFG (_AC(1, ULL) << 17) >> +#define X86_XCR0_TILE_DATA (_AC(1, ULL) << 18) > ... I'm wondering if you deliberately left out APX (bit 19). It was deliberate. APX isn't in the SDM yet, so in principle is still subject to change. I've tweaked the commit message to avoid using the word 'missing'. > Since you're re-doing some of what I have long had in patches already, > I'd also like to ask whether the last underscores each in the two AMX > names really are useful in your opinion. While rebasing isn't going > to be difficult either way, it would be yet simpler with > X86_XCR0_TILECFG and X86_XCR0_TILEDATA, as I've had it in my patches > for over 3 years. I'm torn here. I don't want to deliberately make things harder for you, but I would really prefer that we use the more legible form... >> --- a/xen/arch/x86/xstate.c >> +++ b/xen/arch/x86/xstate.c >> @@ -604,9 +604,156 @@ static bool valid_xcr0(uint64_t xcr0) >> if ( !(xcr0 & X86_XCR0_BNDREGS) != !(xcr0 & X86_XCR0_BNDCSR) ) >> return false; >> >> + /* TILE_CFG and TILE_DATA must be the same. */ >> + if ( !(xcr0 & X86_XCR0_TILE_CFG) != !(xcr0 & X86_XCR0_TILE_DATA) ) >> + return false; >> + >> return true; >> } >> >> +struct xcheck_state { >> + uint64_t states; >> + uint32_t uncomp_size; >> + uint32_t comp_size; >> +}; >> + >> +static void __init check_new_xstate(struct xcheck_state *s, uint64_t new) >> +{ >> + uint32_t hw_size; >> + >> + BUILD_BUG_ON(X86_XCR0_STATES & X86_XSS_STATES); >> + >> + BUG_ON(s->states & new); /* States only increase. */ >> + BUG_ON(!valid_xcr0(s->states | new)); /* Xen thinks it's a good value. */ >> + BUG_ON(new & ~(X86_XCR0_STATES | X86_XSS_STATES)); /* Known state. */ >> + BUG_ON((new & X86_XCR0_STATES) && >> + (new & X86_XSS_STATES)); /* User or supervisor, not both. */ >> + >> + s->states |= new; >> + if ( new & X86_XCR0_STATES ) >> + { >> + if ( !set_xcr0(s->states & X86_XCR0_STATES) ) >> + BUG(); >> + } >> + else >> + set_msr_xss(s->states & X86_XSS_STATES); >> + >> + /* >> + * Check the uncompressed size. Some XSTATEs are out-of-order and fill in >> + * prior holes in the state area, so we check that the size doesn't >> + * decrease. >> + */ >> + hw_size = cpuid_count_ebx(0xd, 0); >> + >> + if ( hw_size < s->uncomp_size ) >> + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, uncompressed hw size %#x < prev size %#x\n", >> + s->states, &new, hw_size, s->uncomp_size); >> + >> + s->uncomp_size = hw_size; >> + >> + /* >> + * Check the compressed size, if available. All components strictly >> + * appear in index order. In principle there are no holes, but some >> + * components have their base address 64-byte aligned for efficiency >> + * reasons (e.g. AMX-TILE) and there are other components small enough to >> + * fit in the gap (e.g. PKRU) without increasing the overall length. >> + */ >> + hw_size = cpuid_count_ebx(0xd, 1); >> + >> + if ( cpu_has_xsavec ) >> + { >> + if ( hw_size < s->comp_size ) >> + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, compressed hw size %#x < prev size %#x\n", >> + s->states, &new, hw_size, s->comp_size); >> + >> + s->comp_size = hw_size; >> + } >> + else >> + BUG_ON(hw_size); /* Compressed size reported, but no XSAVEC ? */ > I'm not quite happy with this being fatal to booting. Maybe just WARN_ON()? It's going to trigger on every pass. I've reworked it to be an opencoded WARN_ONCE() (as we don't have this construct yet), but it's ended up as a plain WARN(). ~Andrew
diff --git a/xen/arch/x86/include/asm/x86-defns.h b/xen/arch/x86/include/asm/x86-defns.h index 48d7a3b7af45..d7602ab225c4 100644 --- a/xen/arch/x86/include/asm/x86-defns.h +++ b/xen/arch/x86/include/asm/x86-defns.h @@ -77,7 +77,7 @@ #define X86_CR4_PKS 0x01000000 /* Protection Key Supervisor */ /* - * XSTATE component flags in XCR0 + * XSTATE component flags in XCR0 | MSR_XSS */ #define X86_XCR0_FP_POS 0 #define X86_XCR0_FP (1ULL << X86_XCR0_FP_POS) @@ -95,11 +95,34 @@ #define X86_XCR0_ZMM (1ULL << X86_XCR0_ZMM_POS) #define X86_XCR0_HI_ZMM_POS 7 #define X86_XCR0_HI_ZMM (1ULL << X86_XCR0_HI_ZMM_POS) +#define X86_XSS_PROC_TRACE (_AC(1, ULL) << 8) #define X86_XCR0_PKRU_POS 9 #define X86_XCR0_PKRU (1ULL << X86_XCR0_PKRU_POS) +#define X86_XSS_PASID (_AC(1, ULL) << 10) +#define X86_XSS_CET_U (_AC(1, ULL) << 11) +#define X86_XSS_CET_S (_AC(1, ULL) << 12) +#define X86_XSS_HDC (_AC(1, ULL) << 13) +#define X86_XSS_UINTR (_AC(1, ULL) << 14) +#define X86_XSS_LBR (_AC(1, ULL) << 15) +#define X86_XSS_HWP (_AC(1, ULL) << 16) +#define X86_XCR0_TILE_CFG (_AC(1, ULL) << 17) +#define X86_XCR0_TILE_DATA (_AC(1, ULL) << 18) #define X86_XCR0_LWP_POS 62 #define X86_XCR0_LWP (1ULL << X86_XCR0_LWP_POS) +#define X86_XCR0_STATES \ + (X86_XCR0_FP | X86_XCR0_SSE | X86_XCR0_YMM | X86_XCR0_BNDREGS | \ + X86_XCR0_BNDCSR | X86_XCR0_OPMASK | X86_XCR0_ZMM | \ + X86_XCR0_HI_ZMM | X86_XCR0_PKRU | X86_XCR0_TILE_CFG | \ + X86_XCR0_TILE_DATA | \ + X86_XCR0_LWP) + +#define X86_XSS_STATES \ + (X86_XSS_PROC_TRACE | X86_XSS_PASID | X86_XSS_CET_U | \ + X86_XSS_CET_S | X86_XSS_HDC | X86_XSS_UINTR | X86_XSS_LBR | \ + X86_XSS_HWP | \ + 0) + /* * Debug status flags in DR6. * diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c index 75788147966a..33a5a89719ef 100644 --- a/xen/arch/x86/xstate.c +++ b/xen/arch/x86/xstate.c @@ -604,9 +604,156 @@ static bool valid_xcr0(uint64_t xcr0) if ( !(xcr0 & X86_XCR0_BNDREGS) != !(xcr0 & X86_XCR0_BNDCSR) ) return false; + /* TILE_CFG and TILE_DATA must be the same. */ + if ( !(xcr0 & X86_XCR0_TILE_CFG) != !(xcr0 & X86_XCR0_TILE_DATA) ) + return false; + return true; } +struct xcheck_state { + uint64_t states; + uint32_t uncomp_size; + uint32_t comp_size; +}; + +static void __init check_new_xstate(struct xcheck_state *s, uint64_t new) +{ + uint32_t hw_size; + + BUILD_BUG_ON(X86_XCR0_STATES & X86_XSS_STATES); + + BUG_ON(s->states & new); /* States only increase. */ + BUG_ON(!valid_xcr0(s->states | new)); /* Xen thinks it's a good value. */ + BUG_ON(new & ~(X86_XCR0_STATES | X86_XSS_STATES)); /* Known state. */ + BUG_ON((new & X86_XCR0_STATES) && + (new & X86_XSS_STATES)); /* User or supervisor, not both. */ + + s->states |= new; + if ( new & X86_XCR0_STATES ) + { + if ( !set_xcr0(s->states & X86_XCR0_STATES) ) + BUG(); + } + else + set_msr_xss(s->states & X86_XSS_STATES); + + /* + * Check the uncompressed size. Some XSTATEs are out-of-order and fill in + * prior holes in the state area, so we check that the size doesn't + * decrease. + */ + hw_size = cpuid_count_ebx(0xd, 0); + + if ( hw_size < s->uncomp_size ) + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, uncompressed hw size %#x < prev size %#x\n", + s->states, &new, hw_size, s->uncomp_size); + + s->uncomp_size = hw_size; + + /* + * Check the compressed size, if available. All components strictly + * appear in index order. In principle there are no holes, but some + * components have their base address 64-byte aligned for efficiency + * reasons (e.g. AMX-TILE) and there are other components small enough to + * fit in the gap (e.g. PKRU) without increasing the overall length. + */ + hw_size = cpuid_count_ebx(0xd, 1); + + if ( cpu_has_xsavec ) + { + if ( hw_size < s->comp_size ) + panic("XSTATE 0x%016"PRIx64", new bits {%63pbl}, compressed hw size %#x < prev size %#x\n", + s->states, &new, hw_size, s->comp_size); + + s->comp_size = hw_size; + } + else + BUG_ON(hw_size); /* Compressed size reported, but no XSAVEC ? */ +} + +/* + * The {un,}compressed XSTATE sizes are reported by dynamic CPUID value, based + * on the current %XCR0 and MSR_XSS values. The exact layout is also feature + * and vendor specific. Cross-check Xen's understanding against real hardware + * on boot. + * + * Testing every combination is prohibitive, so we use a partial approach. + * Starting with nothing active, we add new XSTATEs and check that the CPUID + * dynamic values never decreases. + */ +static void __init noinline xstate_check_sizes(void) +{ + uint64_t old_xcr0 = get_xcr0(); + uint64_t old_xss = get_msr_xss(); + struct xcheck_state s = {}; + + /* + * User XSTATEs, increasing by index. + * + * Chronologically, Intel and AMD had identical layouts for AVX (YMM). + * AMD introduced LWP in Fam15h, following immediately on from YMM. Intel + * left an LWP-shaped hole when adding MPX (BND{CSR,REGS}) in Skylake. + * AMD removed LWP in Fam17h, putting PKRU in the same space, breaking + * layout compatibility with Intel and having a knock-on effect on all + * subsequent states. + */ + check_new_xstate(&s, X86_XCR0_SSE | X86_XCR0_FP); + + if ( cpu_has_avx ) + check_new_xstate(&s, X86_XCR0_YMM); + + if ( cpu_has_mpx ) + check_new_xstate(&s, X86_XCR0_BNDCSR | X86_XCR0_BNDREGS); + + if ( cpu_has_avx512f ) + check_new_xstate(&s, X86_XCR0_HI_ZMM | X86_XCR0_ZMM | X86_XCR0_OPMASK); + + if ( cpu_has_pku ) + check_new_xstate(&s, X86_XCR0_PKRU); + + if ( boot_cpu_has(X86_FEATURE_AMX_TILE) ) + check_new_xstate(&s, X86_XCR0_TILE_DATA | X86_XCR0_TILE_CFG); + + if ( boot_cpu_has(X86_FEATURE_LWP) ) + check_new_xstate(&s, X86_XCR0_LWP); + + /* + * Supervisor XSTATEs, increasing by index. + * + * Intel Broadwell in particular had Processor Trace but no XSAVES. There + * doesn't appear to have been a new enumeration when X86_XSS_PROC_TRACE + * was introduced in Skylake. + */ + if ( cpu_has_xsaves ) + { + if ( cpu_has_proc_trace ) + check_new_xstate(&s, X86_XSS_PROC_TRACE); + + if ( boot_cpu_has(X86_FEATURE_ENQCMD) ) + check_new_xstate(&s, X86_XSS_PASID); + + if ( boot_cpu_has(X86_FEATURE_CET_SS) || + boot_cpu_has(X86_FEATURE_CET_IBT) ) + { + check_new_xstate(&s, X86_XSS_CET_U); + check_new_xstate(&s, X86_XSS_CET_S); + } + + if ( boot_cpu_has(X86_FEATURE_UINTR) ) + check_new_xstate(&s, X86_XSS_UINTR); + + if ( boot_cpu_has(X86_FEATURE_ARCH_LBR) ) + check_new_xstate(&s, X86_XSS_LBR); + } + + /* Restore old state now the test is done. */ + if ( !set_xcr0(old_xcr0) ) + BUG(); + if ( cpu_has_xsaves ) + set_msr_xss(old_xss); +} + /* Collect the information of processor's extended state */ void xstate_init(struct cpuinfo_x86 *c) { @@ -683,6 +830,9 @@ void xstate_init(struct cpuinfo_x86 *c) if ( setup_xstate_features(bsp) && bsp ) BUG(); + + if ( IS_ENABLED(CONFIG_DEBUG) && bsp ) + xstate_check_sizes(); } int validate_xstate(const struct domain *d, uint64_t xcr0, uint64_t xcr0_accum, diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h index 6627453e3985..d9eba5e9a714 100644 --- a/xen/include/public/arch-x86/cpufeatureset.h +++ b/xen/include/public/arch-x86/cpufeatureset.h @@ -266,6 +266,7 @@ XEN_CPUFEATURE(IBPB_RET, 8*32+30) /*A IBPB clears RSB/RAS too. */ XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /*A AVX512 Neural Network Instructions */ XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A AVX512 Multiply Accumulation Single Precision */ XEN_CPUFEATURE(FSRM, 9*32+ 4) /*A Fast Short REP MOVS */ +XEN_CPUFEATURE(UINTR, 9*32+ 5) /* User-mode Interrupts */ XEN_CPUFEATURE(AVX512_VP2INTERSECT, 9*32+8) /*a VP2INTERSECT{D,Q} insns */ XEN_CPUFEATURE(SRBDS_CTRL, 9*32+ 9) /* MSR_MCU_OPT_CTRL and RNGDS_MITG_DIS. */ XEN_CPUFEATURE(MD_CLEAR, 9*32+10) /*!A| VERW clears microarchitectural buffers */ @@ -274,8 +275,10 @@ XEN_CPUFEATURE(TSX_FORCE_ABORT, 9*32+13) /* MSR_TSX_FORCE_ABORT.RTM_ABORT */ XEN_CPUFEATURE(SERIALIZE, 9*32+14) /*A SERIALIZE insn */ XEN_CPUFEATURE(HYBRID, 9*32+15) /* Heterogeneous platform */ XEN_CPUFEATURE(TSXLDTRK, 9*32+16) /*a TSX load tracking suspend/resume insns */ +XEN_CPUFEATURE(ARCH_LBR, 9*32+19) /* Architectural Last Branch Record */ XEN_CPUFEATURE(CET_IBT, 9*32+20) /* CET - Indirect Branch Tracking */ XEN_CPUFEATURE(AVX512_FP16, 9*32+23) /*A AVX512 FP16 instructions */ +XEN_CPUFEATURE(AMX_TILE, 9*32+24) /* AMX Tile architecture */ XEN_CPUFEATURE(IBRSB, 9*32+26) /*A IBRS and IBPB support (used by Intel) */ XEN_CPUFEATURE(STIBP, 9*32+27) /*A STIBP */ XEN_CPUFEATURE(L1D_FLUSH, 9*32+28) /*S MSR_FLUSH_CMD and L1D flush. */
Right now, xstate_ctxt_size() performs a cross-check of size with CPUID in for every call. This is expensive, being used for domain create/migrate, as well as to service certain guest CPUID instructions. Instead, arrange to check the sizes once at boot. See the code comments for details. Right now, it just checks hardware against the algorithm expectations. Later patches will add further cross-checking. Introduce the missing X86_XCR0_* and X86_XSS_* constants, and a couple of missing CPUID bits. This is to maximise coverage in the sanity check, even if we don't expect to use/virtualise some of these features any time soon. Leave HDC and HWP alone for now. We don't have CPUID bits from them stored nicely. Only perform the cross-checks in debug builds. It's only developers or new hardware liable to trip these checks, and Xen at least tracks "maximum value ever seen in xcr0" for the lifetime of the VM, which we don't want to be tickling in the general case. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Roger Pau Monné <roger.pau@citrix.com> v3: * New On Sapphire Rapids with the whole series inc diagnostics, we get this pattern: (XEN) *** check_new_xstate(, 0x00000003) (XEN) *** check_new_xstate(, 0x00000004) (XEN) *** check_new_xstate(, 0x000000e0) (XEN) *** check_new_xstate(, 0x00000200) (XEN) *** check_new_xstate(, 0x00060000) (XEN) *** check_new_xstate(, 0x00000100) (XEN) *** check_new_xstate(, 0x00000400) (XEN) *** check_new_xstate(, 0x00000800) (XEN) *** check_new_xstate(, 0x00001000) (XEN) *** check_new_xstate(, 0x00004000) (XEN) *** check_new_xstate(, 0x00008000) and on Genoa, this pattern: (XEN) *** check_new_xstate(, 0x00000003) (XEN) *** check_new_xstate(, 0x00000004) (XEN) *** check_new_xstate(, 0x000000e0) (XEN) *** check_new_xstate(, 0x00000200) (XEN) *** check_new_xstate(, 0x00000800) (XEN) *** check_new_xstate(, 0x00001000) --- xen/arch/x86/include/asm/x86-defns.h | 25 +++- xen/arch/x86/xstate.c | 150 ++++++++++++++++++++ xen/include/public/arch-x86/cpufeatureset.h | 3 + 3 files changed, 177 insertions(+), 1 deletion(-)