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Re: [Xen-devel] [PATCH v3 33/38] arm/p2m: Add altp2m paging mechanism
Hello Sergej,
On 16/08/16 23:17, Sergej Proskurin wrote:
This commit adds the function "altp2m_lazy_copy" implementing the altp2m
paging mechanism. The function "altp2m_lazy_copy" lazily copies the
hostp2m's mapping into the currently active altp2m view on 2nd stage
translation faults on instruction or data access.
Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
v3: Cosmetic fixes.
Locked hostp2m in the function "altp2m_lazy_copy" to avoid a mapping
being changed in hostp2m before it has been inserted into the
valtp2m view.
Removed unnecessary calls to "p2m_mem_access_check" in the functions
"do_trap_instr_abort_guest" and "do_trap_data_abort_guest" after a
translation fault has been handled by the function
"altp2m_lazy_copy".
Adapted "altp2m_lazy_copy" to return the value "true" if the
encountered translation fault encounters a valid entry inside of the
currently active altp2m view. If multiple vcpu's are using the same
altp2m, it is likely that both generate a translation fault, whereas
the first one will be already handled by "altp2m_lazy_copy". With
this change the 2nd vcpu will retry accessing the faulting address.
Changed order of altp2m checking and MMIO emulation within the
function "do_trap_data_abort_guest". Now, altp2m is checked and
handled only if the MMIO does not have to be emulated.
Changed the function prototype of "altp2m_lazy_copy". This commit
removes the unnecessary struct p2m_domain* from the previous
function prototype. Also, this commit removes the unnecessary
argument gva. Finally, this commit changes the address of the
function parameter gpa from paddr_t to gfn_t and renames it to gfn.
Moved the altp2m handling mechanism into a separate function
"try_handle_altp2m".
Moved the functions "p2m_altp2m_check" and
"altp2m_switch_vcpu_altp2m_by_id" out of this patch.
Moved applied code movement into a separate patch.
---
xen/arch/arm/altp2m.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
xen/arch/arm/traps.c | 35 +++++++++++++++++++++++++
xen/include/asm-arm/altp2m.h | 5 ++++
3 files changed, 102 insertions(+)
diff --git a/xen/arch/arm/altp2m.c b/xen/arch/arm/altp2m.c
index 11272e9..2009bad 100644
--- a/xen/arch/arm/altp2m.c
+++ b/xen/arch/arm/altp2m.c
@@ -165,6 +165,68 @@ out:
return rc;
}
+/*
+ * The function altp2m_lazy_copy returns "false" on error. The return value
+ * "true" signals that either the mapping has been successfully lazy-copied
+ * from the hostp2m to the currently active altp2m view or that the altp2m view
+ * holds already a valid mapping. The latter is the case if multiple vcpu's
+ * using the same altp2m view generate a translation fault that is led back in
+ * both cases to the same mapping and the first fault has been already handled.
+ */
+bool_t altp2m_lazy_copy(struct vcpu *v,
+ gfn_t gfn,
+ struct npfec npfec)
Please don't introduce parameters that are not used at all.
+{
+ struct domain *d = v->domain;
+ struct p2m_domain *hp2m = p2m_get_hostp2m(d), *ap2m = NULL;
+ p2m_type_t p2mt;
+ p2m_access_t p2ma;
+ mfn_t mfn;
+ unsigned int page_order;
+ int rc;
+
+ ap2m = altp2m_get_altp2m(v);
+ if ( ap2m == NULL)
+ return false;
+
+ /* Check if entry is part of the altp2m view. */
+ mfn = p2m_lookup_attr(ap2m, gfn, NULL, NULL, NULL);
+ if ( !mfn_eq(mfn, INVALID_MFN) )
+ /*
+ * If multiple vcpu's are using the same altp2m, it is likely that both
s/vcpu's/vcpus/
+ * generate a translation fault, whereas the first one will be handled
+ * successfully and the second will encounter a valid mapping that has
+ * already been added as a result of the previous translation fault.
+ * In this case, the 2nd vcpu need to retry accessing the faulting
s/need/needs/
+ * address.
+ */
+ return true;
+
+ /*
+ * Lock hp2m to prevent the hostp2m to change a mapping before it is added
+ * to the altp2m view.
+ */
+ p2m_read_lock(hp2m);
+
+ /* Check if entry is part of the host p2m view. */
+ mfn = p2m_lookup_attr(hp2m, gfn, &p2mt, &p2ma, &page_order);
+ if ( mfn_eq(mfn, INVALID_MFN) )
+ goto out;
+
+ rc = modify_altp2m_entry(ap2m, gfn, mfn, p2mt, p2ma, page_order);
+ if ( rc )
+ {
+ gdprintk(XENLOG_ERR, "altp2m[%d] failed to set entry for %#"PRI_gfn" ->
%#"PRI_mfn"\n",
p2midx is unsigned so this should be %u.
+ altp2m_vcpu(v).p2midx, gfn_x(gfn), mfn_x(mfn));
+ domain_crash(hp2m->domain);
You already have the domain in hand with 'd'.
+ }
+
+out:
+ p2m_read_unlock(hp2m);
+
+ return true;
+}
+
static inline void altp2m_reset(struct p2m_domain *p2m)
{
p2m_write_lock(p2m);
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 0bf1653..a4c923c 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -48,6 +48,8 @@
#include <asm/vgic.h>
#include <asm/cpuerrata.h>
+#include <asm/altp2m.h>
+
/* The base of the stack must always be double-word aligned, which means
* that both the kernel half of struct cpu_user_regs (which is pushed in
* entry.S) and struct cpu_info (which lives at the bottom of a Xen
@@ -2397,6 +2399,24 @@ static inline bool hpfar_is_valid(bool s1ptw, uint8_t
fsc)
return s1ptw || (fsc == FSC_FLT_TRANS && !check_workaround_834220());
}
+static bool_t try_handle_altp2m(struct vcpu *v,
+ paddr_t gpa,
+ struct npfec npfec)
I am not convinced about the usefulness of this function.
+{
+ bool_t rc = false;
+
+ if ( altp2m_active(v->domain) )
I might be worth to include an unlikely in altp2m_active to tell the
compiler that altp2m is not the main path.
+ /*
+ * Copy the mapping of the faulting address into the currently
+ * active altp2m view. Return true on success or if the particular
+ * mapping has already been lazily copied to the currently active
+ * altp2m view by another vcpu. Return false otherwise.
+ */
+ rc = altp2m_lazy_copy(v, _gfn(paddr_to_pfn(gpa)), npfec);
+
+ return rc;
+}
+
static void do_trap_instr_abort_guest(struct cpu_user_regs *regs,
const union hsr hsr)
{
@@ -2445,6 +2465,14 @@ static void do_trap_instr_abort_guest(struct
cpu_user_regs *regs,
break;
case FSC_FLT_TRANS:
/*
+ * The guest shall retry accessing the page if the altp2m handler
+ * succeeds. Otherwise, we continue injecting an instruction abort
+ * exception.
+ */
+ if ( try_handle_altp2m(current, gpa, npfec) )
+ return;
I would have expected that altp2m is the last thing we want to check in
the abort handler. I.e after p2m_lookup.
+
+ /*
* The PT walk may have failed because someone was playing
* with the Stage-2 page table. Walk the Stage-2 PT to check
* if the entry exists. If it's the case, return to the guest
@@ -2547,6 +2575,13 @@ static void do_trap_data_abort_guest(struct
cpu_user_regs *regs,
}
/*
+ * The guest shall retry accessing the page if the altp2m handler
+ * succeeds. Otherwise, we continue injecting a data abort exception.
+ */
+ if ( try_handle_altp2m(current, info.gpa, npfec) )
+ return;
Ditto here.
+
+ /*
* The PT walk may have failed because someone was playing
* with the Stage-2 page table. Walk the Stage-2 PT to check
* if the entry exists. If it's the case, return to the guest
diff --git a/xen/include/asm-arm/altp2m.h b/xen/include/asm-arm/altp2m.h
index ef80829..8e40c45 100644
--- a/xen/include/asm-arm/altp2m.h
+++ b/xen/include/asm-arm/altp2m.h
@@ -84,6 +84,11 @@ int altp2m_set_mem_access(struct domain *d,
p2m_access_t a,
gfn_t gfn);
+/* Alternate p2m paging mechanism. */
+bool_t altp2m_lazy_copy(struct vcpu *v,
+ gfn_t gfn,
+ struct npfec npfec);
+
/* Propagates changes made to hostp2m to affected altp2m views. */
int altp2m_propagate_change(struct domain *d,
gfn_t sgfn,
Regards,
--
Julien Grall
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