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d="scan'208";a="62888867" From: Andrew Cooper To: Xen-devel CC: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Wei Liu , Jun Nakajima , Kevin Tian Subject: [PATCH] x86/vmx: Fold VMCS logic in vmx_{get,set}_segment_register() Date: Fri, 21 Jan 2022 11:08:34 +0000 Message-ID: <20220121110834.9143-1-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.11.0 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1642763378947100001 Xen's segment enumeration almost matches the VMCS encoding order, while the VMCS encoding order has the system segments immediately following the user segments for all relevant attributes. Use a sneaky xor to hide the difference in encoding order to fold the switch statements, dropping 10 __vmread() and 10 __vmwrite() calls. Bloat-o-meter reports: add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-433 (-433) Function old new delta vmx_set_segment_register 804 593 -211 vmx_get_segment_register 778 556 -222 showing that these wrappers aren't trivial. In addition, 20 BUGs worth of metadata are dropped. No functional change. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 CC: Wei Liu CC: Jun Nakajima CC: Kevin Tian We could make x86_seg_* match the VMCS encoding order if we're willing to m= ake v->arch.hvm.vmx.vm86_saved_seg[] one entry longer, but I don't think the ad= ded complexity to the vmx_realmode logic is worth it. --- xen/arch/x86/hvm/vmx/vmx.c | 77 ++++++++++++++++++++----------------------= ---- 1 file changed, 34 insertions(+), 43 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index c44cf8f5d425..9765cfd90a0a 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -986,6 +986,7 @@ static void vmx_get_segment_register(struct vcpu *v, en= um x86_segment seg, struct segment_register *reg) { unsigned long attr =3D 0, sel =3D 0, limit; + unsigned int tmp_seg; =20 /* * We may get here in the context of dump_execstate(), which may have @@ -1009,34 +1010,34 @@ static void vmx_get_segment_register(struct vcpu *v= , enum x86_segment seg, return; } =20 - switch ( seg ) + /* + * Xen's x86_seg_* enumeration *almost* matches the VMCS encoding orde= r. + * + * tr and ldtr are reversed, and other areas of code rely on this, so = we + * can't just re-enumerate. + */ + BUILD_BUG_ON(x86_seg_tr !=3D 6); + BUILD_BUG_ON(x86_seg_ldtr !=3D 7); + BUILD_BUG_ON(x86_seg_gdtr !=3D 8); + BUILD_BUG_ON(x86_seg_idtr !=3D 9); + switch ( tmp_seg =3D seg ) { - case x86_seg_es ... x86_seg_gs: - __vmread(GUEST_SEG_SELECTOR(seg), &sel); - __vmread(GUEST_SEG_LIMIT(seg), &limit); - __vmread(GUEST_SEG_BASE(seg), ®->base); - __vmread(GUEST_SEG_AR_BYTES(seg), &attr); - break; case x86_seg_tr: - __vmread(GUEST_TR_SELECTOR, &sel); - __vmread(GUEST_TR_LIMIT, &limit); - __vmread(GUEST_TR_BASE, ®->base); - __vmread(GUEST_TR_AR_BYTES, &attr); - break; + case x86_seg_ldtr: + tmp_seg ^=3D 1; /* Flip tr and ldtr so GUEST_SEG_*() works. */ + fallthrough; + + case x86_seg_es ... x86_seg_gs: + __vmread(GUEST_SEG_SELECTOR(tmp_seg), &sel); + __vmread(GUEST_SEG_AR_BYTES(tmp_seg), &attr); + fallthrough; + case x86_seg_gdtr: - __vmread(GUEST_GDTR_LIMIT, &limit); - __vmread(GUEST_GDTR_BASE, ®->base); - break; case x86_seg_idtr: - __vmread(GUEST_IDTR_LIMIT, &limit); - __vmread(GUEST_IDTR_BASE, ®->base); - break; - case x86_seg_ldtr: - __vmread(GUEST_LDTR_SELECTOR, &sel); - __vmread(GUEST_LDTR_LIMIT, &limit); - __vmread(GUEST_LDTR_BASE, ®->base); - __vmread(GUEST_LDTR_AR_BYTES, &attr); + __vmread(GUEST_SEG_LIMIT(tmp_seg), &limit); + __vmread(GUEST_SEG_BASE(tmp_seg), ®->base); break; + default: BUG(); return; @@ -1150,32 +1151,22 @@ static void vmx_set_segment_register(struct vcpu *v= , enum x86_segment seg, =20 switch ( seg ) { + case x86_seg_tr: + case x86_seg_ldtr: + seg ^=3D 1; /* Flip tr and ldtr so GUEST_SEG_*() works. */ + fallthrough; + case x86_seg_es ... x86_seg_gs: __vmwrite(GUEST_SEG_SELECTOR(seg), sel); - __vmwrite(GUEST_SEG_LIMIT(seg), limit); - __vmwrite(GUEST_SEG_BASE(seg), base); __vmwrite(GUEST_SEG_AR_BYTES(seg), attr); - break; - case x86_seg_tr: - __vmwrite(GUEST_TR_SELECTOR, sel); - __vmwrite(GUEST_TR_LIMIT, limit); - __vmwrite(GUEST_TR_BASE, base); - __vmwrite(GUEST_TR_AR_BYTES, attr); - break; + fallthrough; + case x86_seg_gdtr: - __vmwrite(GUEST_GDTR_LIMIT, limit); - __vmwrite(GUEST_GDTR_BASE, base); - break; case x86_seg_idtr: - __vmwrite(GUEST_IDTR_LIMIT, limit); - __vmwrite(GUEST_IDTR_BASE, base); - break; - case x86_seg_ldtr: - __vmwrite(GUEST_LDTR_SELECTOR, sel); - __vmwrite(GUEST_LDTR_LIMIT, limit); - __vmwrite(GUEST_LDTR_BASE, base); - __vmwrite(GUEST_LDTR_AR_BYTES, attr); + __vmwrite(GUEST_SEG_LIMIT(seg), limit); + __vmwrite(GUEST_SEG_BASE(seg), base); break; + default: BUG(); } --=20 2.11.0