From mboxrd@z Thu Jan 1 00:00:00 1970 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 98FBA19D07A for ; Fri, 29 Aug 2025 20:47:27 +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=1756500449; cv=none; b=kuho8r0JKytQi4CQjUKzQwsz0NCDN5cAzBnKZO3eDhgPxODp82hB7fWrcBIURZUb22lRbHpWMdiB182W3Vwjf3+eS2yEUHse/sVGx5TdbAx9nCxt6CnLkI4rUcDie3Gg3wlWj6meGgLAKVUcKApXZNg8c9vYvTL8rbCOzS304qk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756500449; c=relaxed/simple; bh=9/wSQP4TwiwA28VHXselfVMpk5vyfA21xkhCwpAOusE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=o6ycT2lEMCkDsQ8ZbKKK8SL6g3K9YkcHszJDdfXbxFstV20jtehq40VYIpwHdKeX0TiKGoNKSv1TzvHdAmCAbnzFR/mnrko3hRYeTX6AS5L96DN64/ZEwAZNslGPsbsGqjTJRbccPgpfmdoS8q0w1nZ0UjXFAC4l7vv5i7b6t6E= 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=ToTXahfk; 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="ToTXahfk" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-3235e45b815so2945190a91.0 for ; Fri, 29 Aug 2025 13:47:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1756500447; x=1757105247; 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=AVbLrwfcaMKrZbEzaIUXHMFK+4ezBC1s3sCq6svjQiA=; b=ToTXahfkCYPpuJQrCIJeiRR5rqJCIKh6WcDOebynZAu/Q0ehA7GR0Bznd2eRotavRe AbLqSnKkMd0N3juuERwUg2VP5bdIAuckkWMHjkxgoEfyJL2Hrnx9gcVfEmidVcF7upx6 tFqJXbJ66veK7tk/GGy6w07rO6H0F8jlzpmKqG/Gl5slyefwPKAr4GN2HDndlrASvddd XN0HkOUmj8z0DWMuiKXzFwfmLBUkqrO7NraAqPEA/yuzAf5y4REJVs7Z3hn+1ho9ACFR NbbTb+dv2O5+xnF87FNxyvvHrYwn76gsV4OK2rH/QyloI2g4Yv+/abyzl6bbZwYj3syp X0Dw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756500447; x=1757105247; 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=AVbLrwfcaMKrZbEzaIUXHMFK+4ezBC1s3sCq6svjQiA=; b=MR8WNUlDD1sSUhULsTeEhbw7f833fN+5sTGXuAOpwHXjBvhXHSNS3etYDLl1WlEIcU QETBcqyLnF8seM8lNzRA7RzMqGSm0rFIa9naYfFEldG6LTQL5Mb4+bHWdTdBrJ4rfNWL wtQIKvLpCzeE4pE+8bf5+qEcXadOOCK6YBtFxF9mY8YeXu6/q98+V0FX1O9bbTA+hbtD 4AO1SRBGY2FnsoaBlpsGF1dMYA1Dv+2X6E7Gae/JuhDitZ3UcR1qSA/mkpzkLxT694bK /6ITPOltKFg4VHNrQOntqXPoOGekW6ZC/g4nqWswEMAjjCRPMGIF4bDkMXHP4IPjxtZw 7sAw== X-Forwarded-Encrypted: i=1; AJvYcCWF8IkGqHMZfigecWeF9+GmrMP+w08mC+cSijsKkfRQZAdjabUDnwXd1RqYHJ6IsYqnKrk=@vger.kernel.org X-Gm-Message-State: AOJu0Yxnxy6uFhrt4ol1Wy36sPt0/CxN4MNQaUdm2wRcHr1uhFEuXtPS i7QQ2YHMwaUn9XZACWv5xganZH8DjUN93hiPAkgbEn4dlf3AKETs602qLri6zWqAQdI3ZROZfyM QF8m8DQ== X-Google-Smtp-Source: AGHT+IEEqHXHhC1dOfepFQ4McJBotwArzkUulxIcLhYJ/fKtpfgV5WqeosCA+M558p3CNkr7r/wGr0do/qg= X-Received: from pjbli2.prod.google.com ([2002:a17:90b:48c2:b0:31f:2a78:943]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3889:b0:327:b30d:9b7f with SMTP id 98e67ed59e1d1-327b30d9cdbmr12852743a91.12.1756500446915; Fri, 29 Aug 2025 13:47:26 -0700 (PDT) Date: Fri, 29 Aug 2025 13:47:25 -0700 In-Reply-To: <20250829-pmu_event_info-v5-6-9dca26139a33@rivosinc.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250829-pmu_event_info-v5-0-9dca26139a33@rivosinc.com> <20250829-pmu_event_info-v5-6-9dca26139a33@rivosinc.com> Message-ID: Subject: Re: [PATCH v5 6/9] KVM: Add a helper function to check if a gpa is in writable memselot From: Sean Christopherson To: Atish Patra Cc: Anup Patel , Will Deacon , Mark Rutland , Paul Walmsley , Palmer Dabbelt , Mayuresh Chitale , linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org Content-Type: text/plain; charset="us-ascii" On Fri, Aug 29, 2025, Atish Patra wrote: > The arch specific code may need to know if a particular gpa is valid and > writable for the shared memory between the host and the guest. Currently, > there are few places where it is used in RISC-V implementation. Given the > nature of the function it may be used for other architectures. > Hence, a common helper function is added. > > Suggested-by: Sean Christopherson > Signed-off-by: Atish Patra > --- > include/linux/kvm_host.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 15656b7fba6c..eec5cbbcb4b3 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1892,6 +1892,14 @@ static inline bool kvm_is_gpa_in_memslot(struct kvm *kvm, gpa_t gpa) > return !kvm_is_error_hva(hva); > } > > +static inline bool kvm_is_gpa_in_writable_memslot(struct kvm *kvm, gpa_t gpa) > +{ > + bool writable; > + unsigned long hva = gfn_to_hva_prot(kvm, gpa_to_gfn(gpa), &writable); > + > + return !kvm_is_error_hva(hva) && writable; I don't hate this API, but I don't love it either. Because knowing that the _memslot_ is writable doesn't mean all that much. E.g. in this usage: hva = kvm_vcpu_gfn_to_hva_prot(vcpu, shmem >> PAGE_SHIFT, &writable); if (kvm_is_error_hva(hva) || !writable) return SBI_ERR_INVALID_ADDRESS; ret = kvm_vcpu_write_guest(vcpu, shmem, &zero_sta, sizeof(zero_sta)); if (ret) return SBI_ERR_FAILURE; the error code returned to the guest will be different if the memslot is read-only versus if the VMA is read-only (or not even mapped!). Unless every read-only memslot is explicitly communicated as such to the guest, I don't see how the guest can *know* that a memslot is read-only, so returning INVALID_ADDRESS in that case but not when the underlying VMA isn't writable seems odd. It's also entirely possible the memslot could be replaced with a read-only memslot after the check, or vice versa, i.e. become writable after being rejected. Is it *really* a problem to return FAILURE if the guest attempts to setup steal-time in a read-only memslot? I.e. why not do this and call it good? if (!kvm_is_gpa_in_memslot(vcpu->kvm, shmem >> PAGE_SHIFT)) return SBI_ERR_INVALID_ADDRESS; ret = kvm_vcpu_write_guest(vcpu, shmem, &zero_sta, sizeof(zero_sta)); if (ret) return SBI_ERR_FAILURE;