From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 634E1372063; Fri, 26 Jun 2026 21:44:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782510286; cv=none; b=KpnDINO5hcDzpH8QmcX6SmrSdjQAB1AvGLcy6oj53/Klam7PAUkmAJU6b7KNDD+eK2XSTHi8Hejhl2+dOCFsHsrIarMosZy3FAnxcnSIlXros4uGoAbpZjzy8HHuv2aLH+GBthsyb5hZtDCyyZruKbcuFC4GvteVoSoTRX8GKBU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782510286; c=relaxed/simple; bh=TMfdYLWa6jHJIP4gqNPJcB43oRhnDCqgw8DULZPcChc=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=UCDGj6FS+6nHFAW+4CFstAyCCgBLvK5GTZifnXFO8MsjAPI3FtYsRSry0BCIQo9oZk6aBR1r50v4NQeMJ4PD5N/QQ6z/XRzjdvj/v6jrWfK7bBSZshV+zvY0znsExYHbw3znkq8T8GGnERHHZWccmOY27kjdlBedKWcb13EppS4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C+cygxuN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C+cygxuN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C52711F000E9; Fri, 26 Jun 2026 21:44:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782510285; bh=yUjwzxR9D3gk8N0nZW0RzZjaqCR4SW8ZFywmKyRYiZA=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=C+cygxuNWZGrH9SOdD6atPYapiuwtiJEiL/8CEksuqLQwtJDSOXTq+wbcZia7ehtm vn8fG591w1ClOr1HhlE76sbkumRq0h+Fznb2azGlmBFNnvhTkWjp6MOrZTfP4M+6if VnoUp/8XsOwmgDngnKVFe+A5rUD+90sD8S+x/HbZ19/28ooTJpg2ZTHRVR5UP0/+Wr cb4eHdHb+F4Iu8/a0G7oZzBNsT2iqsFu7XkA2/0iSh8BP1eK4AXqvSWPIOnqTpVRvO YeHJLOL53YxjV4WizYiwT888/WNurHx4+JDCltcwFC39wNDdyUoNX/aVVlbQf4N8QS kdnWrHUDZoMHA== From: sashiko-bot@kernel.org Subject: Re: [PATCH v8 06/20] KVM: selftests: Add helper to generate random u64 in range [min,max] Reply-To: sashiko-reviews@lists.linux.dev To: "Sean Christopherson" Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, "Marc Zyngier" , "Oliver Upton" In-Reply-To: <20260626213534.3866178-7-seanjc@google.com> References: <20260626213534.3866178-1-seanjc@google.com> <20260626213534.3866178-7-seanjc@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 26 Jun 2026 21:44:44 +0000 Message-Id: <20260626214444.C52711F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [Medium] kvm_random_u64() never sets bits 31 and 63, causing kvm_random_u= 64_in_range() to have severe blind spots. -- commit 5a3dcffb3cb35a622072ea5194b7875f774cb3a7 Author: Josh Hilke KVM: selftests: Add helper to generate random u64 in range [min,max] =20 Introduce kvm_random_u64_in_range(state, min, max) to return a random u64=20 within an inclusive range. > diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/= selftests/kvm/lib/test_util.c > index e98ca7ef439c4..e208a57f190cf 100644 > --- a/tools/testing/selftests/kvm/lib/test_util.c > +++ b/tools/testing/selftests/kvm/lib/test_util.c [ ... ] > @@ -42,6 +42,24 @@ u32 kvm_random_u32(struct kvm_random_state *state) > return state->seed; > } > =20 > +/* Returns a random u64 in the inclusive range [min, max] */ > +u64 kvm_random_u64_in_range(struct kvm_random_state *state, u64 min, > + u64 max) > +{ > + u64 value; > + u64 range; > + > + TEST_ASSERT(min <=3D max, "PEBKAC, min =3D 0x%lx, max =3D 0x%lx", min, = max); > + > + value =3D kvm_random_u64(state); [Severity: Medium] Will this result in severe blind spots within the generated range? Looking at how the random value is constructed: tools/testing/selftests/kvm/include/test_util.h:kvm_random_u64() { return ((u64)kvm_random_u32(state) << 32) | kvm_random_u32(state); } And considering kvm_random_u32() limits its return value with a modulo of=20 ((u32)(1 << 31) - 1), it appears bits 31 and 63 will always remain zero. Does this mean the subsequent modulo operation in this function: > + > + range =3D max - min; > + if (range =3D=3D ULLONG_MAX) > + return value; > + > + return min + (value % (range + 1)); > +} will fail to cover large portions of requested ranges? For example, if a=20 test requests a 4GB range, could this only ever return values in the lower= =20 2GB of that range? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260626213534.3866= 178-1-seanjc@google.com?part=3D6