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Mon, 2 Nov 2026 10:14:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1793643294; bh=27pau5S5uokMsAT08PVwL/ml+3ox+5UnlnMf+zd9nAM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XHn6qwUivwORTbvbj3zwkMBmp6GPU2w0yg1eXw+6tuZjPHCY4NcA9WflRxR7olJzu L4tyoWX8mqa88oEfLCQF2nLaBWEbqeVvnmSJn4zpTibWWcSWCBwR3qHuqbtVaIui/x +dPnfBTjr0Jd4UfqDLVhXew36zqYA4zPIgoATLeE= From: Leonardo Bras To: Oliver Upton Cc: Leonardo Bras , kvmarm@lists.linux.dev, Marc Zyngier , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Wei-Lin Chang , Steffen Eiden , Fuad Tabba Subject: Re: [PATCH v2 07/28] KVM: arm64: nv: Set dirty state at stage-2 Date: Mon, 2 Nov 2026 18:14:49 +0000 Message-ID: X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261023205610.1044532-8-oupton@kernel.org> References: <20261023205610.1044532-1-oupton@kernel.org> <20261023205610.1044532-8-oupton@kernel.org> X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit On Fri, Oct 23, 2026 at 01:55:49PM -0700, Oliver Upton wrote: > Set the dirty state on descriptors at stage-2 for write accesses when > DBM is set. > > Signed-off-by: Oliver Upton > --- > arch/arm64/kvm/nested.c | 51 +++++++++++++++++++++++++++++++---------- > 1 file changed, 39 insertions(+), 12 deletions(-) > > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index dea5c31f10df..1d581d3bd557 100644 > --- a/arch/arm64/kvm/nested.c > +++ b/arch/arm64/kvm/nested.c > @@ -151,6 +151,7 @@ struct s2_walk_info { > unsigned int t0sz; > bool be; > bool ha; > + bool hd; > }; > > struct s2_walk_step { > @@ -246,6 +247,20 @@ static int read_guest_s2_desc(struct kvm_vcpu *vcpu, struct s2_walk_step *ws, > return 0; > } > > +static bool should_set_dirty_state(struct s2_walk_info *wi, struct s2_walk_step *ws, > + struct kvm_s2_trans *out, struct kvm_walk_access *access) > +{ > + switch (access->type) { > + /* R_ZYGHJ */ > + case WALK_ACCESS_CMO: > + case WALK_ACCESS_AT: > + return false; > + default: > + /* R_NSXRD */ > + return access->write && wi->hd && out->writable; > + } > +} > + > static int handle_desc_update(struct kvm_vcpu *vcpu, struct s2_walk_info *wi, > struct s2_walk_step *ws, struct kvm_s2_trans *out, > struct kvm_walk_access *access) > @@ -258,6 +273,9 @@ static int handle_desc_update(struct kvm_vcpu *vcpu, struct s2_walk_info *wi, > if (wi->ha) > new |= KVM_PTE_LEAF_ATTR_LO_S2_AF; > > + if (should_set_dirty_state(wi, ws, out, access)) > + new |= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W; > + > if (old == new) > return 0; > > @@ -272,11 +290,15 @@ static int handle_desc_update(struct kvm_vcpu *vcpu, struct s2_walk_info *wi, > } > > ret = __kvm_at_swap_desc(vcpu->kvm, ws->desc_pa, old, new); > - if (!ret || ret == -EAGAIN) > + if (ret == -EAGAIN) > return ret; > + if (!ret) { > + out->desc = ws->desc; > + out->dirty = out->desc & KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W; > + return 0; > + } > > out->esr = ESR_ELx_FSC_SEA_TTW(ws->level); > - out->desc = ws->desc; > return 1; > } Before that out->desc would only be updated if __kvm_at_swap_desc() returned != (0 or -EAGAIN). Now it only gets updated if ret == 0. Is this intentional? > > @@ -422,16 +444,6 @@ static int walk_nested_s2_pgd(struct kvm_vcpu *vcpu, struct kvm_walk_access *acc > return 1; > } > > - ret = handle_desc_update(vcpu, wi, &ws, out, access); > - if (ret) > - return ret; > - > - if (!(ws.desc & KVM_PTE_LEAF_ATTR_LO_S2_AF)) { > - out->esr = compute_fsc(ws.level, ESR_ELx_FSC_ACCESS); > - out->desc = ws.desc; > - return 1; > - } > - > addr_bottom += contiguous_bit_shift(ws.desc, wi, ws.level); > > /* Calculate and return the result */ > @@ -441,6 +453,20 @@ static int walk_nested_s2_pgd(struct kvm_vcpu *vcpu, struct kvm_walk_access *acc > compute_s2_permissions(vcpu, wi, &ws, out); > out->level = ws.level; > out->desc = ws.desc; > + > + ret = handle_desc_update(vcpu, wi, &ws, out, access); > + if (ret) > + return ret; > + > + if (!(ws.desc & KVM_PTE_LEAF_ATTR_LO_S2_AF)) { > + *out = (struct kvm_s2_trans) { > + .esr = compute_fsc(ws.level, ESR_ELx_FSC_ACCESS), > + .desc = ws.desc, > + }; > + > + return 1; > + } > + > return 0; > } The block got moved down in walk_nested_s2_pgd(), and IIUC if the descriptor lacks the AF, we zero all other fields except esr and desc, cleaning everything that just got set in the lines above (out->writable, etc). Any particular reason for doing it like this, instead of keeping where it was, and avoid calculating the other out->* fields? > > @@ -537,6 +563,7 @@ static void setup_s2_walk(struct kvm_vcpu *vcpu, struct s2_walk_info *wi) > ps_to_output_size(FIELD_GET(VTCR_EL2_PS_MASK, vtcr), false)); > wi->ha = vtcr & VTCR_EL2_HA; > wi->be = vcpu_read_sys_reg(vcpu, SCTLR_EL2) & SCTLR_ELx_EE; > + wi->hd = wi->ha && (vtcr & VTCR_EL2_HD); > } > > int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, struct kvm_walk_access *access, > -- > 2.47.3 > Thanks! Leo