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Tue, 13 Aug 2024 07:21:39 -0700 (PDT) From: Alejandro Vallejo To: Xen-devel Cc: Alejandro Vallejo , Jan Beulich , Andrew Cooper , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Subject: [PATCH v3 1/2] x86/fpu: Combine fpu_ctxt and xsave_area in arch_vcpu Date: Tue, 13 Aug 2024 15:21:18 +0100 Message-ID: <20240813142119.29012-2-alejandro.vallejo@cloud.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240813142119.29012-1-alejandro.vallejo@cloud.com> References: <20240813142119.29012-1-alejandro.vallejo@cloud.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @cloud.com) X-ZM-MESSAGEID: 1723558924568116600 Content-Type: text/plain; charset="utf-8" fpu_ctxt is either a pointer to the legacy x87/SSE save area (used by FXSAV= E) or a pointer aliased with xsave_area that points to its fpu_sse subfield. Such subfield is at the base and is identical in size and layout to the legacy buffer. This patch merges the 2 pointers in the arch_vcpu into a single XSAVE area.= In the very rare case in which the host doesn't support XSAVE all we're doing = is wasting a tiny amount of memory and trading those for a lot more simplicity= in the code. Signed-off-by: Alejandro Vallejo --- v3: * Reverse memcpy() and BUILD_BUG_ON() * Use sizeof(arg) rather than sizeof(type) --- xen/arch/x86/domctl.c | 6 ++++- xen/arch/x86/hvm/emulate.c | 4 +-- xen/arch/x86/hvm/hvm.c | 6 ++++- xen/arch/x86/i387.c | 45 +++++-------------------------- xen/arch/x86/include/asm/domain.h | 8 +++--- xen/arch/x86/x86_emulate/blk.c | 3 ++- xen/arch/x86/xstate.c | 13 ++++++--- 7 files changed, 34 insertions(+), 51 deletions(-) diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c index 68b5b46d1a83..63fbceac0911 100644 --- a/xen/arch/x86/domctl.c +++ b/xen/arch/x86/domctl.c @@ -1344,7 +1344,11 @@ void arch_get_info_guest(struct vcpu *v, vcpu_guest_= context_u c) #define c(fld) (c.nat->fld) #endif =20 - memcpy(&c.nat->fpu_ctxt, v->arch.fpu_ctxt, sizeof(c.nat->fpu_ctxt)); + BUILD_BUG_ON(sizeof(c.nat->fpu_ctxt) !=3D + sizeof(v->arch.xsave_area->fpu_sse)); + memcpy(&c.nat->fpu_ctxt, &v->arch.xsave_area->fpu_sse, + sizeof(c.nat->fpu_ctxt)); + if ( is_pv_domain(d) ) c(flags =3D v->arch.pv.vgc_flags & ~(VGCF_i387_valid|VGCF_in_kerne= l)); else diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c index feb4792cc567..03020542c3ba 100644 --- a/xen/arch/x86/hvm/emulate.c +++ b/xen/arch/x86/hvm/emulate.c @@ -2363,7 +2363,7 @@ static int cf_check hvmemul_get_fpu( alternative_vcall(hvm_funcs.fpu_dirty_intercept); else if ( type =3D=3D X86EMUL_FPU_fpu ) { - const fpusse_t *fpu_ctxt =3D curr->arch.fpu_ctxt; + const fpusse_t *fpu_ctxt =3D &curr->arch.xsave_area->fpu_sse; =20 /* * Latch current register state so that we can back out changes @@ -2403,7 +2403,7 @@ static void cf_check hvmemul_put_fpu( =20 if ( aux ) { - fpusse_t *fpu_ctxt =3D curr->arch.fpu_ctxt; + fpusse_t *fpu_ctxt =3D &curr->arch.xsave_area->fpu_sse; bool dval =3D aux->dval; int mode =3D hvm_guest_x86_mode(curr); =20 diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index f49e29faf753..76bbb645b77a 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -916,7 +916,11 @@ static int cf_check hvm_save_cpu_ctxt(struct vcpu *v, = hvm_domain_context_t *h) =20 if ( v->fpu_initialised ) { - memcpy(ctxt.fpu_regs, v->arch.fpu_ctxt, sizeof(ctxt.fpu_regs)); + BUILD_BUG_ON(sizeof(ctxt.fpu_regs) !=3D + sizeof(v->arch.xsave_area->fpu_sse)); + memcpy(ctxt.fpu_regs, &v->arch.xsave_area->fpu_sse, + sizeof(ctxt.fpu_regs)); + ctxt.flags =3D XEN_X86_FPU_INITIALISED; } =20 diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c index 134e0bece519..fbb9d3584a3d 100644 --- a/xen/arch/x86/i387.c +++ b/xen/arch/x86/i387.c @@ -39,7 +39,7 @@ static inline void fpu_xrstor(struct vcpu *v, uint64_t ma= sk) /* Restore x87 FPU, MMX, SSE and SSE2 state */ static inline void fpu_fxrstor(struct vcpu *v) { - const fpusse_t *fpu_ctxt =3D v->arch.fpu_ctxt; + const fpusse_t *fpu_ctxt =3D &v->arch.xsave_area->fpu_sse; =20 /* * Some CPUs don't save/restore FDP/FIP/FOP unless an exception @@ -151,7 +151,7 @@ static inline void fpu_xsave(struct vcpu *v) /* Save x87 FPU, MMX, SSE and SSE2 state */ static inline void fpu_fxsave(struct vcpu *v) { - fpusse_t *fpu_ctxt =3D v->arch.fpu_ctxt; + fpusse_t *fpu_ctxt =3D &v->arch.xsave_area->fpu_sse; unsigned int fip_width =3D v->domain->arch.x87_fip_width; =20 if ( fip_width !=3D 4 ) @@ -212,7 +212,7 @@ void vcpu_restore_fpu_nonlazy(struct vcpu *v, bool need= _stts) * above) we also need to restore full state, to prevent subsequently * saving state belonging to another vCPU. */ - if ( v->arch.fully_eager_fpu || (v->arch.xsave_area && xstate_all(v)) ) + if ( v->arch.fully_eager_fpu || xstate_all(v) ) { if ( cpu_has_xsave ) fpu_xrstor(v, XSTATE_ALL); @@ -299,44 +299,14 @@ void save_fpu_enable(void) /* Initialize FPU's context save area */ int vcpu_init_fpu(struct vcpu *v) { - int rc; - v->arch.fully_eager_fpu =3D opt_eager_fpu; - - if ( (rc =3D xstate_alloc_save_area(v)) !=3D 0 ) - return rc; - - if ( v->arch.xsave_area ) - v->arch.fpu_ctxt =3D &v->arch.xsave_area->fpu_sse; - else - { - BUILD_BUG_ON(__alignof(v->arch.xsave_area->fpu_sse) < 16); - v->arch.fpu_ctxt =3D _xzalloc(sizeof(v->arch.xsave_area->fpu_sse), - __alignof(v->arch.xsave_area->fpu_sse)= ); - if ( v->arch.fpu_ctxt ) - { - fpusse_t *fpu_sse =3D v->arch.fpu_ctxt; - - fpu_sse->fcw =3D FCW_DEFAULT; - fpu_sse->mxcsr =3D MXCSR_DEFAULT; - } - else - rc =3D -ENOMEM; - } - - return rc; + return xstate_alloc_save_area(v); } =20 void vcpu_setup_fpu(struct vcpu *v, struct xsave_struct *xsave_area, const void *data, unsigned int fcw_default) { - /* - * For the entire function please note that vcpu_init_fpu() (above) po= ints - * v->arch.fpu_ctxt into v->arch.xsave_area when XSAVE is available. H= ence - * accesses through both pointers alias one another, and the shorter f= orm - * is used here. - */ - fpusse_t *fpu_sse =3D v->arch.fpu_ctxt; + fpusse_t *fpu_sse =3D &v->arch.xsave_area->fpu_sse; =20 ASSERT(!xsave_area || xsave_area =3D=3D v->arch.xsave_area); =20 @@ -373,10 +343,7 @@ void vcpu_setup_fpu(struct vcpu *v, struct xsave_struc= t *xsave_area, /* Free FPU's context save area */ void vcpu_destroy_fpu(struct vcpu *v) { - if ( v->arch.xsave_area ) - xstate_free_save_area(v); - else - xfree(v->arch.fpu_ctxt); + xstate_free_save_area(v); } =20 /* diff --git a/xen/arch/x86/include/asm/domain.h b/xen/arch/x86/include/asm/d= omain.h index bca3258d69ac..3da60af2a44a 100644 --- a/xen/arch/x86/include/asm/domain.h +++ b/xen/arch/x86/include/asm/domain.h @@ -592,11 +592,11 @@ struct pv_vcpu struct arch_vcpu { /* - * guest context (mirroring struct vcpu_guest_context) common - * between pv and hvm guests + * Guest context common between PV and HVM guests. Includes general pu= rpose + * registers, segment registers and other parts of the exception frame. + * + * It doesn't contain FPU state, as that lives in xsave_area instead. */ - - void *fpu_ctxt; struct cpu_user_regs user_regs; =20 /* Debug registers. */ diff --git a/xen/arch/x86/x86_emulate/blk.c b/xen/arch/x86/x86_emulate/blk.c index e790f4f90056..28b54f26fe29 100644 --- a/xen/arch/x86/x86_emulate/blk.c +++ b/xen/arch/x86/x86_emulate/blk.c @@ -11,7 +11,8 @@ !defined(X86EMUL_NO_SIMD) # ifdef __XEN__ # include -# define FXSAVE_AREA current->arch.fpu_ctxt +# define FXSAVE_AREA ((struct x86_fxsr *) \ + (void *)¤t->arch.xsave_area->fpu_sse) # else # define FXSAVE_AREA get_fpu_save_area() # endif diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c index 5c4144d55e89..850ee31bd18c 100644 --- a/xen/arch/x86/xstate.c +++ b/xen/arch/x86/xstate.c @@ -507,9 +507,16 @@ int xstate_alloc_save_area(struct vcpu *v) unsigned int size; =20 if ( !cpu_has_xsave ) - return 0; - - if ( !is_idle_vcpu(v) || !cpu_has_xsavec ) + { + /* + * This is bigger than FXSAVE_SIZE by 64 bytes, but it helps treat= ing + * the FPU state uniformly as an XSAVE buffer even if XSAVE is not + * available in the host. 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charset="utf-8" It was trying to do too many things at once and there was no clear way of defining what it was meant to do. This commit splits the function in three. 1. A function to return the FPU to power-on reset values. 2. A function to return the FPU to default values. 3. A x87/SSE state loader (equivalent to the old function when it took a = data pointer). While at it, make sure the abridged tag is consistent with the manuals and start as 0xFF. Signed-off-by: Alejandro Vallejo Reviewed-by: Jan Beulich --- v3: * Adjust commit message, as the split is now in 3. * Remove bulky comment, as the rationale for it turned out to be unsubstantiated. I can't find proof in xen-devel of the stream operating the way I claimed, and at that point having the comment at all is pointless I suspect the rationale for xsave_vcpu(v) was merely to skip writing the XS= AVE header when it would be rewritten later on. Whatever it might be the current logic does the right thing and is several orders of magnitude clearer about= its objective and its intent. --- xen/arch/x86/domain.c | 7 ++-- xen/arch/x86/hvm/hvm.c | 12 +++---- xen/arch/x86/i387.c | 60 +++++++++++++++---------------- xen/arch/x86/include/asm/i387.h | 28 ++++++++++++--- xen/arch/x86/include/asm/xstate.h | 1 + 5 files changed, 62 insertions(+), 46 deletions(-) diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c index d977ec71ca20..5af9e3e7a8b4 100644 --- a/xen/arch/x86/domain.c +++ b/xen/arch/x86/domain.c @@ -1186,9 +1186,10 @@ int arch_set_info_guest( is_pv_64bit_domain(d) ) v->arch.flags &=3D ~TF_kernel_mode; =20 - vcpu_setup_fpu(v, v->arch.xsave_area, - flags & VGCF_I387_VALID ? &c.nat->fpu_ctxt : NULL, - FCW_DEFAULT); + if ( flags & VGCF_I387_VALID ) + vcpu_setup_fpu(v, &c.nat->fpu_ctxt); + else + vcpu_default_fpu(v); =20 if ( !compat ) { diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 76bbb645b77a..95d66e68a849 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -1165,10 +1165,10 @@ static int cf_check hvm_load_cpu_ctxt(struct domain= *d, hvm_domain_context_t *h) seg.attr =3D ctxt.ldtr_arbytes; hvm_set_segment_register(v, x86_seg_ldtr, &seg); =20 - /* Cover xsave-absent save file restoration on xsave-capable host. */ - vcpu_setup_fpu(v, xsave_enabled(v) ? NULL : v->arch.xsave_area, - ctxt.flags & XEN_X86_FPU_INITIALISED ? ctxt.fpu_regs : = NULL, - FCW_RESET); + if ( ctxt.flags & XEN_X86_FPU_INITIALISED ) + vcpu_setup_fpu(v, &ctxt.fpu_regs); + else + vcpu_reset_fpu(v); =20 v->arch.user_regs.rax =3D ctxt.rax; v->arch.user_regs.rbx =3D ctxt.rbx; @@ -4008,9 +4008,7 @@ void hvm_vcpu_reset_state(struct vcpu *v, uint16_t cs= , uint16_t ip) v->arch.guest_table =3D pagetable_null(); } =20 - if ( v->arch.xsave_area ) - v->arch.xsave_area->xsave_hdr.xstate_bv =3D 0; - vcpu_setup_fpu(v, v->arch.xsave_area, NULL, FCW_RESET); + vcpu_reset_fpu(v); =20 arch_vcpu_regs_init(v); v->arch.user_regs.rip =3D ip; diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c index fbb9d3584a3d..f7a9dcd162ba 100644 --- a/xen/arch/x86/i387.c +++ b/xen/arch/x86/i387.c @@ -303,41 +303,37 @@ int vcpu_init_fpu(struct vcpu *v) return xstate_alloc_save_area(v); } =20 -void vcpu_setup_fpu(struct vcpu *v, struct xsave_struct *xsave_area, - const void *data, unsigned int fcw_default) +void vcpu_reset_fpu(struct vcpu *v) { - fpusse_t *fpu_sse =3D &v->arch.xsave_area->fpu_sse; - - ASSERT(!xsave_area || xsave_area =3D=3D v->arch.xsave_area); - - v->fpu_initialised =3D !!data; + v->fpu_initialised =3D false; + *v->arch.xsave_area =3D (struct xsave_struct) { + .fpu_sse =3D { + .mxcsr =3D MXCSR_DEFAULT, + .fcw =3D FCW_RESET, + .ftw =3D FTW_RESET, + }, + .xsave_hdr.xstate_bv =3D X86_XCR0_X87, + }; +} =20 - if ( data ) - { - memcpy(fpu_sse, data, sizeof(*fpu_sse)); - if ( xsave_area ) - xsave_area->xsave_hdr.xstate_bv =3D XSTATE_FP_SSE; - } - else if ( xsave_area && fcw_default =3D=3D FCW_DEFAULT ) - { - xsave_area->xsave_hdr.xstate_bv =3D 0; - fpu_sse->mxcsr =3D MXCSR_DEFAULT; - } - else - { - memset(fpu_sse, 0, sizeof(*fpu_sse)); - fpu_sse->fcw =3D fcw_default; - fpu_sse->mxcsr =3D MXCSR_DEFAULT; - if ( v->arch.xsave_area ) - { - v->arch.xsave_area->xsave_hdr.xstate_bv &=3D ~XSTATE_FP_SSE; - if ( fcw_default !=3D FCW_DEFAULT ) - v->arch.xsave_area->xsave_hdr.xstate_bv |=3D X86_XCR0_X87; - } - } +void vcpu_default_fpu(struct vcpu *v) +{ + v->fpu_initialised =3D false; + *v->arch.xsave_area =3D (struct xsave_struct) { + .fpu_sse =3D { + .mxcsr =3D MXCSR_DEFAULT, + .fcw =3D FCW_DEFAULT, + }, + }; +} =20 - if ( xsave_area ) - xsave_area->xsave_hdr.xcomp_bv =3D 0; +void vcpu_setup_fpu(struct vcpu *v, const void *data) +{ + v->fpu_initialised =3D true; + *v->arch.xsave_area =3D (struct xsave_struct) { + .fpu_sse =3D *(const fpusse_t*)data, + .xsave_hdr.xstate_bv =3D XSTATE_FP_SSE, + }; } =20 /* Free FPU's context save area */ diff --git a/xen/arch/x86/include/asm/i387.h b/xen/arch/x86/include/asm/i38= 7.h index a783549db991..7a69577de45b 100644 --- a/xen/arch/x86/include/asm/i387.h +++ b/xen/arch/x86/include/asm/i387.h @@ -31,10 +31,30 @@ void vcpu_restore_fpu_nonlazy(struct vcpu *v, bool need= _stts); void vcpu_restore_fpu_lazy(struct vcpu *v); void vcpu_save_fpu(struct vcpu *v); void save_fpu_enable(void); - int vcpu_init_fpu(struct vcpu *v); -struct xsave_struct; -void vcpu_setup_fpu(struct vcpu *v, struct xsave_struct *xsave_area, - const void *data, unsigned int fcw_default); void vcpu_destroy_fpu(struct vcpu *v); + +/* + * Restore v's FPU to power-on reset values + * + * @param v vCPU containing the FPU + */ +void vcpu_reset_fpu(struct vcpu *v); + +/* + * Restore v's FPU to default values + * + * @param v vCPU containing the FPU + */ +void vcpu_default_fpu(struct vcpu *v); + +/* + * Load x87/SSE state into v's FPU + * + * Overrides the XSAVE header to set the state components to be x87 and SS= E. + * + * @param v vCPU containing the FPU + * @param data 512-octet blob for x87/SSE state + */ +void vcpu_setup_fpu(struct vcpu *v, const void *data); #endif /* __ASM_I386_I387_H */ diff --git a/xen/arch/x86/include/asm/xstate.h b/xen/arch/x86/include/asm/x= state.h index ebeb2a3dcaf9..6144ed6f8551 100644 --- a/xen/arch/x86/include/asm/xstate.h +++ b/xen/arch/x86/include/asm/xstate.h @@ -14,6 +14,7 @@ =20 #define FCW_DEFAULT 0x037f #define FCW_RESET 0x0040 +#define FTW_RESET 0xFF #define MXCSR_DEFAULT 0x1f80 =20 extern uint32_t mxcsr_mask; --=20 2.45.2