Re: [PATCH V4 22/24] xen/arm: Add mapcache invalidation handling

2021-01-21 Thread Oleksandr 



On 15.01.21 04:11, Stefano Stabellini wrote:

Hi Stefano


On Tue, 12 Jan 2021, Oleksandr Tyshchenko wrote:

From: Oleksandr Tyshchenko 

We need to send mapcache invalidation request to qemu/demu everytime
the page gets removed from a guest.

At the moment, the Arm code doesn't explicitely remove the existing
mapping before inserting the new mapping. Instead, this is done
implicitely by __p2m_set_entry().

So we need to recognize a case when old entry is a RAM page *and*
the new MFN is different in order to set the corresponding flag.
The most suitable place to do this is p2m_free_entry(), there
we can find the correct leaf type. The invalidation request
will be sent in do_trap_hypercall() later on.

Taking into the account the following the do_trap_hypercall()
is the best place to send invalidation request:
  - The only way a guest can modify its P2M on Arm is via an hypercall
  - When sending the invalidation request, the vCPU will be blocked
until all the IOREQ servers have acknowledged the invalidation

Signed-off-by: Oleksandr Tyshchenko 
CC: Julien Grall 
[On Arm only]
Tested-by: Wei Chen 

---
Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

***
Please note, this patch depends on the following which is
on review:
https://patchwork.kernel.org/patch/11803383/

This patch is on par with x86 code (whether it is buggy or not).
If there is a need to improve/harden something, this can be done on
a follow-up.
***

Changes V1 -> V2:
- new patch, some changes were derived from (+ new explanation):
  xen/ioreq: Make x86's invalidate qemu mapcache handling common
- put setting of the flag into __p2m_set_entry()
- clarify the conditions when the flag should be set
- use domain_has_ioreq_server()
- update do_trap_hypercall() by adding local variable

Changes V2 -> V3:
- update patch description
- move check to p2m_free_entry()
- add a comment
- use "curr" instead of "v" in do_trap_hypercall()

Changes V3 -> V4:
- update patch description
- re-order check in p2m_free_entry() to call domain_has_ioreq_server()
  only if p2m->domain == current->domain
- add a comment in do_trap_hypercall()
---
  xen/arch/arm/p2m.c   | 25 +
  xen/arch/arm/traps.c | 20 +---
  2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index d41c4fa..26acb95d 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1,6 +1,7 @@
  #include 
  #include 
  #include 
+#include 
  #include 
  #include 
  #include 
@@ -749,17 +750,25 @@ static void p2m_free_entry(struct p2m_domain *p2m,
  if ( !p2m_is_valid(entry) )
  return;
  
-/* Nothing to do but updating the stats if the entry is a super-page. */

-if ( p2m_is_superpage(entry, level) )
+if ( p2m_is_superpage(entry, level) || (level == 3) )
  {
-p2m->stats.mappings[level]--;
-return;
-}
+#ifdef CONFIG_IOREQ_SERVER
+/*
+ * If this gets called (non-recursively) then either the entry
+ * was replaced by an entry with a different base (valid case) or
+ * the shattering of a superpage was failed (error case).
+ * So, at worst, the spurious mapcache invalidation might be sent.
+ */
+if ( (p2m->domain == current->domain) &&
+  domain_has_ioreq_server(p2m->domain) &&
+  p2m_is_ram(entry.p2m.type) )
+p2m->domain->mapcache_invalidate = true;
+#endif
  
-if ( level == 3 )

-{
  p2m->stats.mappings[level]--;
-p2m_put_l3_page(entry);
+/* Nothing to do if the entry is a super-page. */
+if ( level == 3 )
+p2m_put_l3_page(entry);
  return;
  }
  
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c

index 35094d8..1070d1b 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1443,6 +1443,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, 
register_t *nr,
const union hsr hsr)
  {
  arm_hypercall_fn_t call = NULL;
+struct vcpu *curr = current;
  
  BUILD_BUG_ON(NR_hypercalls < ARRAY_SIZE(arm_hypercall_table) );
  
@@ -1459,7 +1460,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,

  return;
  }
  
-current->hcall_preempted = false;

+curr->hcall_preempted = false;
  
  perfc_incra(hypercalls, *nr);

  call = arm_hypercall_table[*nr].fn;
@@ -1472,7 +1473,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, 
register_t *nr,
  HYPERCALL_RESULT_REG(regs) = call(HYPERCALL_ARGS(regs));
  
  #ifndef NDEBUG

-if ( !current->hcall_preempted )
+if ( !curr->hcall_preempted )
  {
  /* Deliberately corrupt parameter regs used by this hypercall. */
  switch ( arm_hypercall_table[*nr].nr_args ) {
@@ -1489,8 +1490,21 @@ static void

Re: [PATCH V4 22/24] xen/arm: Add mapcache invalidation handling

2021-01-14 Thread Stefano Stabellini 
On Tue, 12 Jan 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko 
> 
> We need to send mapcache invalidation request to qemu/demu everytime
> the page gets removed from a guest.
> 
> At the moment, the Arm code doesn't explicitely remove the existing
> mapping before inserting the new mapping. Instead, this is done
> implicitely by __p2m_set_entry().
> 
> So we need to recognize a case when old entry is a RAM page *and*
> the new MFN is different in order to set the corresponding flag.
> The most suitable place to do this is p2m_free_entry(), there
> we can find the correct leaf type. The invalidation request
> will be sent in do_trap_hypercall() later on.
> 
> Taking into the account the following the do_trap_hypercall()
> is the best place to send invalidation request:
>  - The only way a guest can modify its P2M on Arm is via an hypercall
>  - When sending the invalidation request, the vCPU will be blocked
>until all the IOREQ servers have acknowledged the invalidation
> 
> Signed-off-by: Oleksandr Tyshchenko 
> CC: Julien Grall 
> [On Arm only]
> Tested-by: Wei Chen 
> 
> ---
> Please note, this is a split/cleanup/hardening of Julien's PoC:
> "Add support for Guest IO forwarding to a device emulator"
> 
> ***
> Please note, this patch depends on the following which is
> on review:
> https://patchwork.kernel.org/patch/11803383/
> 
> This patch is on par with x86 code (whether it is buggy or not).
> If there is a need to improve/harden something, this can be done on
> a follow-up.
> ***
> 
> Changes V1 -> V2:
>- new patch, some changes were derived from (+ new explanation):
>  xen/ioreq: Make x86's invalidate qemu mapcache handling common
>- put setting of the flag into __p2m_set_entry()
>- clarify the conditions when the flag should be set
>- use domain_has_ioreq_server()
>- update do_trap_hypercall() by adding local variable
> 
> Changes V2 -> V3:
>- update patch description
>- move check to p2m_free_entry()
>- add a comment
>- use "curr" instead of "v" in do_trap_hypercall()
> 
> Changes V3 -> V4:
>- update patch description
>- re-order check in p2m_free_entry() to call domain_has_ioreq_server()
>  only if p2m->domain == current->domain
>- add a comment in do_trap_hypercall()
> ---
>  xen/arch/arm/p2m.c   | 25 +
>  xen/arch/arm/traps.c | 20 +---
>  2 files changed, 34 insertions(+), 11 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index d41c4fa..26acb95d 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1,6 +1,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -749,17 +750,25 @@ static void p2m_free_entry(struct p2m_domain *p2m,
>  if ( !p2m_is_valid(entry) )
>  return;
>  
> -/* Nothing to do but updating the stats if the entry is a super-page. */
> -if ( p2m_is_superpage(entry, level) )
> +if ( p2m_is_superpage(entry, level) || (level == 3) )
>  {
> -p2m->stats.mappings[level]--;
> -return;
> -}
> +#ifdef CONFIG_IOREQ_SERVER
> +/*
> + * If this gets called (non-recursively) then either the entry
> + * was replaced by an entry with a different base (valid case) or
> + * the shattering of a superpage was failed (error case).
> + * So, at worst, the spurious mapcache invalidation might be sent.
> + */
> +if ( (p2m->domain == current->domain) &&
> +  domain_has_ioreq_server(p2m->domain) &&
> +  p2m_is_ram(entry.p2m.type) )
> +p2m->domain->mapcache_invalidate = true;
> +#endif
>  
> -if ( level == 3 )
> -{
>  p2m->stats.mappings[level]--;
> -p2m_put_l3_page(entry);
> +/* Nothing to do if the entry is a super-page. */
> +if ( level == 3 )
> +p2m_put_l3_page(entry);
>  return;
>  }
>  
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 35094d8..1070d1b 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1443,6 +1443,7 @@ static void do_trap_hypercall(struct cpu_user_regs 
> *regs, register_t *nr,
>const union hsr hsr)
>  {
>  arm_hypercall_fn_t call = NULL;
> +struct vcpu *curr = current;
>  
>  BUILD_BUG_ON(NR_hypercalls < ARRAY_SIZE(arm_hypercall_table) );
>  
> @@ -1459,7 +1460,7 @@ static void do_trap_hypercall(struct cpu_user_regs 
> *regs, register_t *nr,
>  return;
>  }
>  
> -current->hcall_preempted = false;
> +curr->hcall_preempted = false;
>  
>  perfc_incra(hypercalls, *nr);
>  call = arm_hypercall_table[*nr].fn;
> @@ -1472,7 +1473,7 @@ static void do_trap_hypercall(struct cpu_user_regs 
> *regs, register_t *nr,
>  HYPERCALL_RESULT_REG(regs) = call(HYPERCALL_ARGS(regs));
>  
>  #ifndef NDEBUG
> -if ( !current->hcall_preempted )
> +if ( !curr->hcall_preempted )
>  {
>

[PATCH V4 22/24] xen/arm: Add mapcache invalidation handling

2021-01-12 Thread Oleksandr Tyshchenko 
From: Oleksandr Tyshchenko 

We need to send mapcache invalidation request to qemu/demu everytime
the page gets removed from a guest.

At the moment, the Arm code doesn't explicitely remove the existing
mapping before inserting the new mapping. Instead, this is done
implicitely by __p2m_set_entry().

So we need to recognize a case when old entry is a RAM page *and*
the new MFN is different in order to set the corresponding flag.
The most suitable place to do this is p2m_free_entry(), there
we can find the correct leaf type. The invalidation request
will be sent in do_trap_hypercall() later on.

Taking into the account the following the do_trap_hypercall()
is the best place to send invalidation request:
 - The only way a guest can modify its P2M on Arm is via an hypercall
 - When sending the invalidation request, the vCPU will be blocked
   until all the IOREQ servers have acknowledged the invalidation

Signed-off-by: Oleksandr Tyshchenko 
CC: Julien Grall 
[On Arm only]
Tested-by: Wei Chen 

---
Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

***
Please note, this patch depends on the following which is
on review:
https://patchwork.kernel.org/patch/11803383/

This patch is on par with x86 code (whether it is buggy or not).
If there is a need to improve/harden something, this can be done on
a follow-up.
***

Changes V1 -> V2:
   - new patch, some changes were derived from (+ new explanation):
 xen/ioreq: Make x86's invalidate qemu mapcache handling common
   - put setting of the flag into __p2m_set_entry()
   - clarify the conditions when the flag should be set
   - use domain_has_ioreq_server()
   - update do_trap_hypercall() by adding local variable

Changes V2 -> V3:
   - update patch description
   - move check to p2m_free_entry()
   - add a comment
   - use "curr" instead of "v" in do_trap_hypercall()

Changes V3 -> V4:
   - update patch description
   - re-order check in p2m_free_entry() to call domain_has_ioreq_server()
 only if p2m->domain == current->domain
   - add a comment in do_trap_hypercall()
---
 xen/arch/arm/p2m.c   | 25 +
 xen/arch/arm/traps.c | 20 +---
 2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index d41c4fa..26acb95d 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1,6 +1,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -749,17 +750,25 @@ static void p2m_free_entry(struct p2m_domain *p2m,
 if ( !p2m_is_valid(entry) )
 return;
 
-/* Nothing to do but updating the stats if the entry is a super-page. */
-if ( p2m_is_superpage(entry, level) )
+if ( p2m_is_superpage(entry, level) || (level == 3) )
 {
-p2m->stats.mappings[level]--;
-return;
-}
+#ifdef CONFIG_IOREQ_SERVER
+/*
+ * If this gets called (non-recursively) then either the entry
+ * was replaced by an entry with a different base (valid case) or
+ * the shattering of a superpage was failed (error case).
+ * So, at worst, the spurious mapcache invalidation might be sent.
+ */
+if ( (p2m->domain == current->domain) &&
+  domain_has_ioreq_server(p2m->domain) &&
+  p2m_is_ram(entry.p2m.type) )
+p2m->domain->mapcache_invalidate = true;
+#endif
 
-if ( level == 3 )
-{
 p2m->stats.mappings[level]--;
-p2m_put_l3_page(entry);
+/* Nothing to do if the entry is a super-page. */
+if ( level == 3 )
+p2m_put_l3_page(entry);
 return;
 }
 
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 35094d8..1070d1b 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1443,6 +1443,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, 
register_t *nr,
   const union hsr hsr)
 {
 arm_hypercall_fn_t call = NULL;
+struct vcpu *curr = current;
 
 BUILD_BUG_ON(NR_hypercalls < ARRAY_SIZE(arm_hypercall_table) );
 
@@ -1459,7 +1460,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, 
register_t *nr,
 return;
 }
 
-current->hcall_preempted = false;
+curr->hcall_preempted = false;
 
 perfc_incra(hypercalls, *nr);
 call = arm_hypercall_table[*nr].fn;
@@ -1472,7 +1473,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, 
register_t *nr,
 HYPERCALL_RESULT_REG(regs) = call(HYPERCALL_ARGS(regs));
 
 #ifndef NDEBUG
-if ( !current->hcall_preempted )
+if ( !curr->hcall_preempted )
 {
 /* Deliberately corrupt parameter regs used by this hypercall. */
 switch ( arm_hypercall_table[*nr].nr_args ) {
@@ -1489,8 +1490,21 @@ static void do_trap_hypercall(struct cpu_user_regs 
*regs, register_t *nr,
 #endif
 
 /* Ensure the hypercall trap instruction is re-executed. */
-if (