From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 7AA0816F8EF for ; Tue, 3 Sep 2024 15:09:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725376183; cv=none; b=PIadzAuIDwHBYjvIJn7/rAYeQBX+l8q9IM/ehMOqYWF41VwpTWtgURuLwl3UFukDgGMTg9ZnmuBcIuDbmL5AkPWy8V4S9JEZGeFVwJlM7pTFE+qkA0OtJpGKcx/xK0O267XHaJ0we+uUeJ75K7EMa5Or842DzGh++yfxgOqTAU4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725376183; c=relaxed/simple; bh=hkihc/6WA9/QhPK1a/f1doLwTM/grTsynAcwgS7nw/8=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=CLRRio2kN7rTlnqtJeA5/io0suHJZXD2hv16KDHPZKB4yhhju2PyShKLALV5rPS75DrMD3bbNMfSwzGEI5heL4aUkZ8l6bHUmENMMI/J0DMSjslYW69pNxVP4oc9Vd5iEF3IAwNGY10hQ0xUjnsIsMLVt5CTMp0Bx7dLbngMkws= 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=HqLTVqY5; arc=none smtp.client-ip=209.85.214.202 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="HqLTVqY5" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-20537e42b7aso43701925ad.2 for ; Tue, 03 Sep 2024 08:09:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1725376182; x=1725980982; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=gfCufivpzBm6oAcRdCpegQIb7KEtzf8TXvjWVp3MAlg=; b=HqLTVqY52kE7mUwfcS4lD5rF99E2nbBFwyQ606yEaNijZMen8Jx0SEO/4T5tKFytt8 PRqBpgZIytsma9yk6qZ96PROhA+q/B+R2yN8Q+7qpXtXHaLKgh4ykV30LXJa6JoMtUhf 3NJWh6bbQxVeE7gJBJqyvXPv2sxyAk3wJwzZK/HUxKqRdGgPaa8+1dtbZLug3Ano/iVT 69bMyuFvISKsqSpCnmv8CyJVFUBkm++R8xXaSwyJTnoEbxE9Dv/PGFxhe9W6MbYUS3iB VHEl6CBrpHqRuRQiC7yLfWiq10zdva7b1Pk/rZ0wz1NGox7BShyL2aL/IPs/vkpLR3sM Wk8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1725376182; x=1725980982; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=gfCufivpzBm6oAcRdCpegQIb7KEtzf8TXvjWVp3MAlg=; b=eqXWGv7oBS8SarY2ByQFiRBnT7hwHTeeJ+e6xcUzKdetTbAVIilvlNUXShO4aCq7nL Ak5MMXgwcxq7UdxN2vMEqQaFtkuy1YnSxKAHav4AJGmHYUBmDA0MwOSxtGuEiCO/mqsL NgaIm/Ca46iyAzanp5gyzJgV1IxS2KdcctcXjP+G7WiJNWn6LfpNriu9x8KebGE5uv6j I8N/5oaeRayGQO5BsMISJGVeaupxI7JkyUX0m51H+8BgKVH0m+fJtAgnqKKtSuJAqQTn wfDoweqcZ82zSFrvBsX012AIKaeXJdwhqiCbxahLPTSv8voGH4txUwnr3c5gamQsRM7T jfpA== X-Forwarded-Encrypted: i=1; AJvYcCXl6EpQD3C9g7wQcGkL9wkpe7ymRpgrVLsJ2HLjvfy8v11CmPvYj1NQolmFMRnD9lIOPvQzwSjezq5cs80=@vger.kernel.org X-Gm-Message-State: AOJu0YzzBC7CegEJeCZt/h1R96ZXYg11WvCSZIaVYRaHbC82wTJcMwTF vOMVYCTmNJAef8uFz6Azin36zybypPCIrW72QSzZ0rTLXnhBMFWCh6JV+pyUML5adQcuEqiwJV6 Diw== X-Google-Smtp-Source: AGHT+IGFfMtNWVn2Os9mP28kanvnTDWaSYvo+LMgHGVIxjM+2irTaxwzoo4qnseusX5LrbYip8qiQXwrCMg= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:903:183:b0:206:8a7c:9197 with SMTP id d9443c01a7336-2068a7c9354mr3683845ad.1.1725376181611; Tue, 03 Sep 2024 08:09:41 -0700 (PDT) Date: Tue, 3 Sep 2024 08:09:40 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240802195120.325560-1-seanjc@google.com> <20240802195120.325560-2-seanjc@google.com> Message-ID: Subject: Re: [PATCH 1/5] KVM: x86: Re-enter guest if WRMSR(X2APIC_ICR) fastpath is successful From: Sean Christopherson To: Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Mon, Sep 02, 2024, Paolo Bonzini wrote: > On Fri, Aug 2, 2024 at 9:51=E2=80=AFPM Sean Christopherson wrote: > > Re-enter the guest in the fastpath if WRMSR emulation for x2APIC's ICR = is > > successful, as no additional work is needed, i.e. there is no code uniq= ue > > for WRMSR exits between the fastpath and the "!=3D EXIT_FASTPATH_NONE" = check > > in __vmx_handle_exit(). >=20 > What about if you send an IPI to yourself? Doesn't that return true > for kvm_vcpu_exit_request() if posted interrupts are disabled? Yes, but that doesn't have anything to do with WRMSR itself, as KVM needs t= o morph EXIT_FASTPATH_EXIT_HANDLED =3D> EXIT_FASTPATH_REENTER_GUEST if there's a pe= nding event that needs requires injection. Given that kvm_x86_ops.sync_pir_to_irr is likely NULL if virtual interrupt = delivery is enabled, the overhead of the trying to re-enter the guest it essentially= a few cycles, e.g. check vcpu->mode and kvm_request_pending().