From nobody Fri Dec 19 14:39:56 2025 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5D12C2144CF for ; Tue, 1 Apr 2025 16:43:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743525805; cv=none; b=JmbC8WdyT8dUyz4qLJTgAcH/vu1vDY/RAEl9TD3C2WYyx+lJraHdDZI8pHBe1a9I17azpQ+aN1Cv4EICbbYzLh9TVlQ/FHvpfrq/162GMQg4i8hSsNTkR2QVMgBXn2DXV+aaBKBTalFnsDFcf0w9QOhgGIGLhAqZHJvPKdcUEpU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743525805; c=relaxed/simple; bh=0mb7W2KJR+X1+iO3XRU17z9B6gV64MNgKjj7DrBL3rQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Zq53z4uowIdV/kDf39b86wDUxyMrHNcKXGUuy0LabEKw824G0R5JyZt8kmovbbZVN7KMWccyGahcmuaU1S07sIBVhviznIH2b3FFog4K685yasCv9TW3j5cF18PoowZNS1F0/J/Gk41ywQdhbb7a/aB2ebFAJcz0MdFXzJFaNSQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=yKTYDGFw; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="yKTYDGFw" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2ff6af1e264so735736a91.3 for ; Tue, 01 Apr 2025 09:43:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1743525803; x=1744130603; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=JvMZfz//CfX9sBYOfMJB+q+wsvNCB9UZGeb1vhxbwqc=; b=yKTYDGFw7VHBl+U+Jw+Xp1PqBR+1bhJZkrct3n/fRHAeZAqn8xA30ig0dm58liStjJ 0HI0d0hdELhixyO8n+di9f2jPcc8HHu/PCNKJ3k+aZFWZDapAnmOhEiOb1nj/YAgTdEs KLBbjsgK0HauVh0/vERpOcvBgPeNChm7TPvHrrjPAdJKtpZgGFiD+KvP4QJhKsMkzGLZ N6qRoNYFjVc36dLSirXnEVPYfV8m8lW48gFarwsJB1BLqzFS8NwEke1vK2whTWooWi7J TKKDOH1clXCd/1FTmkQWNvRoCykjVeYGBr+9gV1eH5B8zcWwhSKWkSgGkexkgrkdxKU0 rmGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1743525803; x=1744130603; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=JvMZfz//CfX9sBYOfMJB+q+wsvNCB9UZGeb1vhxbwqc=; b=GYLQtxMXfe5pTw4EDdtv5BHKgNBigxjp8Gxzppe/uVnwL9W9iaBwKtm6ZMKRoOhFRN LSeJuu9uRIva0x4mFUoXDfNm5EMUlk0Ub/utBkGyK8jddrH562oRQyA589I7Mdf+iWIG JAa1suhaefjLNbv0jrhdQ2KPbLCO7XHShz2+v01zyUAnFA0WHMmz2POswSr0NJC92/RE t/duTGHK3UJ9Dcz3NcDQGAgVaD09QNSs2QXXLgNtAOXb+LVcgDm1mcSuLmnV2fBksG+L SN+vfoGvJelgmI2Rpd0qArSTHNoGiz6TXJEtg/I/lvguXfKmRmoezSJ1T6ukgZi6H3su GcpQ== X-Gm-Message-State: AOJu0YyrrROLwcoBdCKgca6BBF46TP6MPNeSwlO/R/BFEQ0myaZU0h51 UEueeegI2TQ9CJleALgTBiMMZ/fbOZmIGFiTc+G2SPkEx0hd7NN4RDmY3PzuhvD3c2AB6PfRt3o ARA== X-Google-Smtp-Source: AGHT+IFappA+693mpg8zPDSbFvdj433IwkFt3wteT5TPuG94UFq5oeeszFM3n1+NCGeGHcm5eLfjft4ZDV0= X-Received: from pfbhh11.prod.google.com ([2002:a05:6a00:868b:b0:739:485f:c33e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:9f47:b0:1f5:67e2:7790 with SMTP id adf61e73a8af0-2009f606767mr20650362637.17.1743525803622; Tue, 01 Apr 2025 09:43:23 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 1 Apr 2025 09:34:45 -0700 In-Reply-To: <20250401163447.846608-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250401163447.846608-1-seanjc@google.com> X-Mailer: git-send-email 2.49.0.472.ge94155a9ec-goog Message-ID: <20250401163447.846608-7-seanjc@google.com> Subject: [PATCH v2 6/8] KVM: VMX: Isolate pure loads from atomic XCHG when processing PIR From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Sean Christopherson , Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Jim Mattson Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Rework KVM's processing of the PIR to use the same algorithm as posted MSIs, i.e. to do READ(x4) =3D> XCHG(x4) instead of (READ+XCHG)(x4). Given KVM's long-standing, sub-optimal use of 32-bit accesses to the PIR, it's safe to say far more thought and investigation was put into handling the PIR for posted MSIs, i.e. there's no reason to assume KVM's existing logic is meaningful, let alone superior. Matching the processing done by posted MSIs will also allow deduplicating the code between KVM and posted MSIs. See the comment for handle_pending_pir() added by commit 1b03d82ba15e ("x86/irq: Install posted MSI notification handler") for details on why isolating loads from XCHG is desirable. Suggested-by: Jim Mattson Signed-off-by: Sean Christopherson --- arch/x86/kvm/lapic.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index e4f182ee9340..0463e89376fb 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -657,7 +657,7 @@ static u8 count_vectors(void *bitmap) =20 bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr) { - unsigned long pir_vals[NR_PIR_WORDS]; + unsigned long pir_vals[NR_PIR_WORDS], pending =3D 0; u32 *__pir =3D (void *)pir_vals; u32 i, vec; u32 irr_val, prev_irr_val; @@ -668,6 +668,13 @@ bool __kvm_apic_update_irr(unsigned long *pir, void *r= egs, int *max_irr) =20 for (i =3D 0; i < NR_PIR_WORDS; i++) { pir_vals[i] =3D READ_ONCE(pir[i]); + pending |=3D pir_vals[i]; + } + + if (!pending) + return false; + + for (i =3D 0; i < NR_PIR_WORDS; i++) { if (!pir_vals[i]) continue; =20 --=20 2.49.0.472.ge94155a9ec-goog