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[92.22.57.86]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8a6bbesm9616571f8f.12.2025.10.03.15.53.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Oct 2025 15:53:45 -0700 (PDT) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d1e9e9b5-a0ab-11f0-9809-7dc792cee155 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1759532026; x=1760136826; darn=lists.xenproject.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=uU50b2CIr8z+rKB8yhDMf5NI7QoTTkkJ3hl1yF+jo5w=; b=AtVI7h+KoCgniDsNAy29u6TWQqOYGYzD20lBHSAz3fAw5Nk5X0+fY5SKUhL3tThysm gAmu9sVNy8zAGcDjC/VT/+yuRP97hehZM/qlgF3tyMmI6WNtOQQziEw6KEt/e1jWmh7A ZqulECobhXbvdr6C/YWfyPSyssOhbuoQJOWq0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759532026; x=1760136826; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=uU50b2CIr8z+rKB8yhDMf5NI7QoTTkkJ3hl1yF+jo5w=; b=gaeMC1zFy2gZ4QoZFYHpEMUzZnvF2EB/NRQ2RvgF2ItGBoTFRZESRXDLvPBwY0RM2v HRAWGkbZd+7JFIz7/37tVESvpU3Sq8mwbB5lzNbiFgRcm9ICju5Kok5PUl/VlaNcXctN uYO7LcHoSPXvWm/6jm9PKoLdyJyGqw1viVHnGakNShzrjWDw82PnBBgVAkByHvyrG9VB NVn2Ab9MK9YMouJlfL8kOw+jr120p4psK0+rj8SlHBLRd9JgXiQYToQUxFKMM6MWNJCA TwuyLJbfvErG/FMexwxVWdeiAQqiB9ZIJ16XvaFt6CWq5Qtkgja0QK9f+z5MyheC60lW 0ByQ== X-Gm-Message-State: AOJu0YxriTDGUM0qjMdUDpTSdmZpATZZT/7BnIMxL2Tj1Wzdv/JbZ6U0 EuKwIn3XUvpXjHy9NsyPzFQShZRRBx03E5tpKLpTs8/TauhasY1LEpEQziKwKiogHZUCVr+hhEo F7ylvkjz0To6R X-Gm-Gg: ASbGncvPVbo/mU/UojrSTIVUWbOqiHWmEBqkEbg7UT0owgHkaGg84AKUEc3NP3/6xJh 1oumuSOPC3LRKsCdKzLx/HIa03gZkQxctRZA1XMEPqGGm4cu8WV73858XDaBBqZpGBrsH9cDuwt oQykSbcJ4fZMIl/a1kKJH2jSaM98LRhXMGjFHRWgNx0WZiY7sXU+e3TIVR6UeB+UQXVpOvzRtnE R78QzvArMIGj3TWPE/AzQY0H4PITOgUGAzNNAdFCXgH8b81WSkRVp+lUeLvpJWmFLp+vW8sTRdx q7JpMuohYMdzNDKJVouXsfJKVkaqR6DWyeU9gKxfXnF4fZJV0xXH+DLKb0Ii6HL2UsvSsT0rCmP SDpaF3eJKwYtdNKNMR5WScZ7WLFVbKd5P/4GsRjeObUpQg8krFQsY277qE3MksXMxEjBRahHbqz EnUicxw9/w/Bu8DxOYeMoHw1+KIrjkINY= X-Google-Smtp-Source: AGHT+IFNgesRO9KQE+1EDzFOyGemzxgi/B/Bn2ir1u8VhCJcvbxVt8SX2TtWZgCw44x7gKMh2wvVLQ== X-Received: by 2002:a05:6000:40da:b0:3e0:c28a:abbb with SMTP id ffacd0b85a97d-42567158fccmr3269428f8f.13.1759532026367; Fri, 03 Oct 2025 15:53:46 -0700 (PDT) From: Andrew Cooper To: Xen-devel Cc: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Subject: [PATCH v3 05/22] x86/fsgsbase: Improve code generation in read_registers() Date: Fri, 3 Oct 2025 23:53:17 +0100 Message-Id: <20251003225334.2123667-6-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20251003225334.2123667-1-andrew.cooper3@citrix.com> References: <20251003225334.2123667-1-andrew.cooper3@citrix.com> 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: 1759532056722116600 It turns out that using the higher level helpers adjacent like this leads to terrible code generation. Due to -fno-strict-alising, the store into state= -> invalidates the read_cr4() address calculation (which is really cpu_info->c= r4 under the hood), meaning that it can't be hoisted. As a result we get "locate the top of stack block, get cr4, and see if FSGSBASE is set" repeated 3 times, and an unreasoanble number of basic bloc= ks. Hoist the calculation manually, which results in two basic blocks. Signed-off-by: Andrew Cooper Acked-by: Jan Beulich --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 Side-by-side disassembly: https://termbin.com/9xfq --- xen/arch/x86/traps.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index 0c5393cb2166..545c42a10862 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -118,9 +118,18 @@ static void read_registers(struct extra_state *state) state->cr3 =3D read_cr3(); state->cr4 =3D read_cr4(); =20 - state->fsb =3D read_fs_base(); - state->gsb =3D read_gs_base(); - state->gss =3D read_gs_shadow(); + if ( state->cr4 & X86_CR4_FSGSBASE ) + { + state->fsb =3D __rdfsbase(); + state->gsb =3D __rdgsbase(); + state->gss =3D __rdgs_shadow(); + } + else + { + state->fsb =3D rdmsr(MSR_FS_BASE); + state->gsb =3D rdmsr(MSR_GS_BASE); + state->gss =3D rdmsr(MSR_SHADOW_GS_BASE); + } =20 asm ( "mov %%ds, %0" : "=3Dm" (state->ds) ); asm ( "mov %%es, %0" : "=3Dm" (state->es) ); --=20 2.39.5