From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="jQbXGPOb" Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 420D8CB for ; Mon, 11 Dec 2023 14:57:03 -0800 (PST) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-5e16d7537bcso9689677b3.3 for ; Mon, 11 Dec 2023 14:57:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1702335422; x=1702940222; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=XLiTtRRqM+qNBV6tYcuiNPBMTUo4FdzTRXinHk4XXSY=; b=jQbXGPOb4aUz9h/DCAaYw7yu4FgckKWiK+UtCid96tFmLgd1DsXM1Nlg70/QJAgWsg dMahWtxfn21P0gLevEhrT4stbX+G9LgIJb2xHzz65KsFXxG4LoNvMy4psC8j2UNmT4fj pDpbB8+2zOwEUWd4UbKgezZ3mIoTUJzY1QpoCyVK3nxn0HgmAoIfcVCFvIVHy9wWJT1+ 8qOL94SzQGnpyi+G8/RZZnUc/1DtscA5UgcHiyy5RZYsurcyfPlxW5UfrTwLEycq2zTL /0ZrNfsidk4ihm5yEwsYfoFAmsgaFUIokvfc5mLHHoWeIuIlUf27vK0h/eR7iFdLbIy8 Ip+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702335422; x=1702940222; h=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=XLiTtRRqM+qNBV6tYcuiNPBMTUo4FdzTRXinHk4XXSY=; b=S86Cs5X4bowVz7BgC4Fl/rtA93qjJA7P70EvZh3Lo76BwwjnH0idRPjuLLCM3PpwUK 1vQ8nQEZ5fV6oJI/ruAb/ZCeyPtn7TjMAvSAA4sRvAY6Tfp2gTfVI/wt1bEq43/9DHfY wrI1LPZUTXGwj0px2N5R0thELYTTWGgIUN6G8fY6Kk2J2xH8vj6UMDNpRxYn4MVPXStZ pl1iKFsW1S10iAcevxDqBirdOE6YvuXzJUmTAmFhrMZunF743n/ioQkSGOKzEkKz5Ra7 pIKssDODnpQmYBSAhNzj8uI0raYELWeNLnoy9jf89Pnbn4eUU9hgqppT96UN2SSGq9Ux IbxQ== X-Gm-Message-State: AOJu0YyNNq3L0UgdvQ9IZzTlQ8NZtg/Cm90AvLXr2fBELx6tvkGFZTlm UsVRqJ3D3uUfk8zMHSIVj4ieGZinDMw= X-Google-Smtp-Source: AGHT+IEhhypj7D/PwqeFaL95W7v5NUceMg/HzzkyowCvBZn3QIeqdswnpmg0GcBg4W9bI7RZryt2AT+W5iM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:c01:b0:5d1:104a:acb5 with SMTP id cl1-20020a05690c0c0100b005d1104aacb5mr53522ywb.2.1702335422457; Mon, 11 Dec 2023 14:57:02 -0800 (PST) Date: Mon, 11 Dec 2023 14:57:00 -0800 In-Reply-To: <865y16b6cf.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <865y16b6cf.wl-maz@kernel.org> Message-ID: Subject: Re: [PATCH v3 1/5] KVM: Add arch specific interfaces for sampling guest callchains From: Sean Christopherson To: Marc Zyngier Cc: Tianyi Liu , pbonzini@redhat.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, mark.rutland@arm.com, mlevitsk@redhat.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com Content-Type: text/plain; charset="us-ascii" On Sun, Dec 10, 2023, Marc Zyngier wrote: > On Sun, 10 Dec 2023 08:12:18 +0000, Tianyi Liu wrote: > > +bool kvm_arch_vcpu_read_virt(struct kvm_vcpu *vcpu, gva_t addr, void *dest, unsigned int length) > > +{ > > + /* TODO: implement */ > > + return false; > > +} > > I don't do it very often, but the only thing I can say about this is > *NAK*. > > You have decided to ignore the previous review comments, which is your > prerogative. However, I absolutely refuse to add half baked and > *dangerous* stuff to the arm64's version of KVM. > > If you can convince the x86 folks that they absolutely want this, fine > by me. But this need to be a buy-in interface, not something that is > required for each and every architecture to have stubs, wrongly > suggesting that extra work is needed. > > For arm64, the way to go is to have this in userspace. Which is both > easy to implement and safe. And until we have such a userspace > implementation as a baseline, I will not consider a kernel > version. I too want more justification of why this needs to be handled in the kernel[*]. The usefulness of this is dubious for many modern setups/workloads, and outright undesirable for some, e.g. many (most?) cloud providers want to make it all but impossible to access customer data. [*] https://lore.kernel.org/all/ZSlNsn-f1j2bB8pW@FVFF77S0Q05N.cambridge.arm.com