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Re: [PATCH v2 1/3] xen/arm: Add way to disable traps on accesses to unmapped addresses
- To: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Julien Grall <julien@xxxxxxx>
- Date: Thu, 29 May 2025 16:59:21 +0100
- Cc: sstabellini@xxxxxxxxxx, bertrand.marquis@xxxxxxx, michal.orzel@xxxxxxx, Volodymyr_Babchuk@xxxxxxxx, andrew.cooper3@xxxxxxxxxx, edgar.iglesias@xxxxxxx, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 29 May 2025 15:59:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Hi Edgar,
On 29/05/2025 16:50, Edgar E. Iglesias wrote:
From: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxx>
Add a per-domain way to optionally disable traps for accesses
to unmapped addresses.
The domain flag is general but it's only implemented for ARM for now.
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
---
tools/libs/light/libxl_arm.c | 3 +++
xen/arch/arm/dom0less-build.c | 3 +++
xen/arch/arm/domain.c | 3 ++-
xen/arch/arm/domain_build.c | 3 ++-
xen/arch/arm/io.c | 36 +++++++++++++++++++++++++++++++++--
xen/common/domain.c | 3 ++-
xen/include/public/domctl.h | 4 +++-
Looking at the changelog, I saw you removed the go bindings (although,
they were in patch 3). But I don't quite understand why.
Also, I think you need to update the OCaml bindings.
7 files changed, 49 insertions(+), 6 deletions(-)
diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index 75c811053c..9530996e72 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -233,6 +233,9 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
config->arch.sve_vl = d_config->b_info.arch_arm.sve_vl / 128U;
}
+ /* Trap accesses to unmapped areas. */
+ config->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
+
return 0;
}
diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index a49764f0ad..a4e0a33632 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -343,6 +343,9 @@ void __init arch_create_domUs(struct dt_device_node *node,
panic("'sve' property found, but CONFIG_ARM64_SVE not selected\n");
#endif
}
+
+ /* Trap accesses to unmapped areas. */
+ d_cfg->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
}
int __init init_intc_phandle(struct kernel_info *kinfo, const char *name,
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 45aeb8bddc..be58a23dd7 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -612,7 +612,8 @@ int arch_sanitise_domain_config(struct
xen_domctl_createdomain *config)
unsigned int max_vcpus;
unsigned int flags_required = (XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap);
unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu
|
- XEN_DOMCTL_CDF_xs_domain );
+ XEN_DOMCTL_CDF_xs_domain |
+ XEN_DOMCTL_CDF_trap_unmapped_accesses );
unsigned int sve_vl_bits = sve_decode_vl(config->arch.sve_vl);
if ( (config->flags & ~flags_optional) != flags_required )
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index b189a7cfae..7ff9c1b584 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2003,7 +2003,8 @@ void __init create_dom0(void)
{
struct domain *dom0;
struct xen_domctl_createdomain dom0_cfg = {
- .flags = XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap,
+ .flags = XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap |
+ XEN_DOMCTL_CDF_trap_unmapped_accesses,
.max_evtchn_port = -1,
.max_grant_frames = gnttab_dom0_frames(),
.max_maptrack_frames = -1,
diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index 5a4b0e8f25..adfc822e7e 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -21,6 +21,32 @@
#include "decode.h"
+/* Handler for unmapped ranges. Writes ignored, reads return all ones. */
+static int unmapped_read(struct vcpu *v, mmio_info_t *info, register_t *r,
+ void *priv)
+{
+ uint64_t mask = GENMASK_ULL((1U << info->dabt.size) * 8 - 1, 0);
NIT: Looking at the other part of io.c, we are using GENMASK. Any reason
to not use the same?
+
+ /* Mask off upper bits. */
+ *r = UINT64_MAX & mask;
+ return 1;
+}
+
+static int unmapped_write(struct vcpu *v, mmio_info_t *info, register_t r,
+ void *priv)
+{
+ return 1;
+}
+
+static const struct mmio_handler_ops unmapped_ops = {
+ .read = unmapped_read,
+ .write = unmapped_write
+};
+
+static const struct mmio_handler unmapped_handler = {
+ .ops = &unmapped_ops
+};
+
static enum io_state handle_read(const struct mmio_handler *handler,
struct vcpu *v,
mmio_info_t *info)
@@ -175,11 +201,17 @@ enum io_state try_handle_mmio(struct cpu_user_regs *regs,
handler = find_mmio_handler(v->domain, info->gpa);
if ( !handler )
{
+ bool trap_unmapped = v->domain->options &
+ XEN_DOMCTL_CDF_trap_unmapped_accesses;
rc = try_fwd_ioserv(regs, v, info);
if ( rc == IO_HANDLED )
return handle_ioserv(regs, v);
-
- return rc;
+ else if ( rc == IO_UNHANDLED && !trap_unmapped )
+ {
+ /* Fallback to the unmapped handler. */
+ handler = &unmapped_handler;
+ } else
Style:
else if ( ... )
{
}
else
{
}
+ return rc;
}
/*
diff --git a/xen/common/domain.c b/xen/common/domain.c
index abf1969e60..ac4f58f638 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -721,7 +721,8 @@ static int sanitise_domain_config(struct
xen_domctl_createdomain *config)
~(XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap |
XEN_DOMCTL_CDF_s3_integrity | XEN_DOMCTL_CDF_oos_off |
XEN_DOMCTL_CDF_xs_domain | XEN_DOMCTL_CDF_iommu |
- XEN_DOMCTL_CDF_nested_virt | XEN_DOMCTL_CDF_vpmu) )
+ XEN_DOMCTL_CDF_nested_virt | XEN_DOMCTL_CDF_vpmu |
+ XEN_DOMCTL_CDF_trap_unmapped_accesses) )
{
dprintk(XENLOG_INFO, "Unknown CDF flags %#x\n", config->flags);
return -EINVAL;
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 5b2063eed9..be19ab5e26 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -66,9 +66,11 @@ struct xen_domctl_createdomain {
#define XEN_DOMCTL_CDF_nested_virt (1U << _XEN_DOMCTL_CDF_nested_virt)
/* Should we expose the vPMU to the guest? */
#define XEN_DOMCTL_CDF_vpmu (1U << 7)
+/* Should we trap guest accesses to unmapped addresses? */
+#define XEN_DOMCTL_CDF_trap_unmapped_accesses (1U << 8)
/* Max XEN_DOMCTL_CDF_* constant. Used for ABI checking. */
-#define XEN_DOMCTL_CDF_MAX XEN_DOMCTL_CDF_vpmu
+#define XEN_DOMCTL_CDF_MAX XEN_DOMCTL_CDF_trap_unmapped_accesses
uint32_t flags;
--
Julien Grall
|
