* [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-12 14:05 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:05 UTC (permalink / raw)
To: kvmarm
Cc: Pingfan Liu, James Morse, Russell King, Marc Zyngier,
Julien Thierry, Suzuki K Poulose, linux-doc, linux-arm-kernel
Both arm and arm64 kernel entry point have the following prerequisite:
MMU = off, D-cache = off, I-cache = dont care.
HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
new kernel.
Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
off, and KVM resets them when its unload. These are achieved by
HVC_RESET_VECTORS call.
Improve the document.
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
To: kvmarm@lists.cs.columbia.edu
---
Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
index d9eba93..a95bc30 100644
--- a/Documentation/virt/kvm/arm/hyp-abi.rst
+++ b/Documentation/virt/kvm/arm/hyp-abi.rst
@@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
* ::
- r0/x0 = HVC_RESET_VECTORS
+ x0 = HVC_RESET_VECTORS (arm64 only)
- Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
+ Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
stubs' exception vector value. This effectively disables an existing
hypervisor.
@@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
x3 = x1's value when entering the next payload (arm64)
x4 = x2's value when entering the next payload (arm64)
- Mask all exceptions, disable the MMU, move the arguments into place
+ Mask all exceptions, disable the MMU and D-cache, move the arguments into place
(arm64 only), and jump to the restart address while at HYP/EL2. This
hypercall is not expected to return to its caller.
--
2.7.5
^ permalink raw reply related [flat|nested] 12+ messages in thread
* [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-12 14:05 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:05 UTC (permalink / raw)
To: kvmarm
Cc: Marc Zyngier, linux-doc, Russell King, Pingfan Liu, linux-arm-kernel
Both arm and arm64 kernel entry point have the following prerequisite:
MMU = off, D-cache = off, I-cache = dont care.
HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
new kernel.
Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
off, and KVM resets them when its unload. These are achieved by
HVC_RESET_VECTORS call.
Improve the document.
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
To: kvmarm@lists.cs.columbia.edu
---
Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
index d9eba93..a95bc30 100644
--- a/Documentation/virt/kvm/arm/hyp-abi.rst
+++ b/Documentation/virt/kvm/arm/hyp-abi.rst
@@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
* ::
- r0/x0 = HVC_RESET_VECTORS
+ x0 = HVC_RESET_VECTORS (arm64 only)
- Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
+ Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
stubs' exception vector value. This effectively disables an existing
hypervisor.
@@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
x3 = x1's value when entering the next payload (arm64)
x4 = x2's value when entering the next payload (arm64)
- Mask all exceptions, disable the MMU, move the arguments into place
+ Mask all exceptions, disable the MMU and D-cache, move the arguments into place
(arm64 only), and jump to the restart address while at HYP/EL2. This
hypercall is not expected to return to its caller.
--
2.7.5
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
^ permalink raw reply related [flat|nested] 12+ messages in thread
* [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-12 14:05 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:05 UTC (permalink / raw)
To: kvmarm
Cc: Suzuki K Poulose, Marc Zyngier, linux-doc, Russell King,
Pingfan Liu, James Morse, linux-arm-kernel, Julien Thierry
Both arm and arm64 kernel entry point have the following prerequisite:
MMU = off, D-cache = off, I-cache = dont care.
HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
new kernel.
Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
off, and KVM resets them when its unload. These are achieved by
HVC_RESET_VECTORS call.
Improve the document.
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
To: kvmarm@lists.cs.columbia.edu
---
Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
index d9eba93..a95bc30 100644
--- a/Documentation/virt/kvm/arm/hyp-abi.rst
+++ b/Documentation/virt/kvm/arm/hyp-abi.rst
@@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
* ::
- r0/x0 = HVC_RESET_VECTORS
+ x0 = HVC_RESET_VECTORS (arm64 only)
- Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
+ Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
stubs' exception vector value. This effectively disables an existing
hypervisor.
@@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
x3 = x1's value when entering the next payload (arm64)
x4 = x2's value when entering the next payload (arm64)
- Mask all exceptions, disable the MMU, move the arguments into place
+ Mask all exceptions, disable the MMU and D-cache, move the arguments into place
(arm64 only), and jump to the restart address while at HYP/EL2. This
hypercall is not expected to return to its caller.
--
2.7.5
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
2020-08-12 14:05 ` Pingfan Liu
(?)
@ 2020-08-12 14:14 ` Pingfan Liu
-1 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:14 UTC (permalink / raw)
To: kvmarm
Cc: James Morse, Russell King, Marc Zyngier, Julien Thierry,
Suzuki K Poulose, linux-doc, linux-arm-kernel
This issue is detected by Morse
(https://lore.kernel.org/linux-arm-kernel/9b0da257-785b-90ba-de3c-b9ee9ccdeeba@arm.com/)
during the discussion for my patch.
I am not quite sure about the arm, but based on the note at the head
of arm/kernel/head.S, things should go that way. If any mistake,
please correct me.
Thanks,
Pingfan
On Wed, Aug 12, 2020 at 10:05 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
>
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: linux-doc@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> To: kvmarm@lists.cs.columbia.edu
> ---
> Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
>
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
>
> --
> 2.7.5
>
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-12 14:14 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:14 UTC (permalink / raw)
To: kvmarm; +Cc: linux-doc, Marc Zyngier, Russell King, linux-arm-kernel
This issue is detected by Morse
(https://lore.kernel.org/linux-arm-kernel/9b0da257-785b-90ba-de3c-b9ee9ccdeeba@arm.com/)
during the discussion for my patch.
I am not quite sure about the arm, but based on the note at the head
of arm/kernel/head.S, things should go that way. If any mistake,
please correct me.
Thanks,
Pingfan
On Wed, Aug 12, 2020 at 10:05 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
>
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: linux-doc@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> To: kvmarm@lists.cs.columbia.edu
> ---
> Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
>
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
>
> --
> 2.7.5
>
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-12 14:14 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-12 14:14 UTC (permalink / raw)
To: kvmarm
Cc: linux-doc, Marc Zyngier, Suzuki K Poulose, Russell King,
James Morse, linux-arm-kernel, Julien Thierry
This issue is detected by Morse
(https://lore.kernel.org/linux-arm-kernel/9b0da257-785b-90ba-de3c-b9ee9ccdeeba@arm.com/)
during the discussion for my patch.
I am not quite sure about the arm, but based on the note at the head
of arm/kernel/head.S, things should go that way. If any mistake,
please correct me.
Thanks,
Pingfan
On Wed, Aug 12, 2020 at 10:05 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
>
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: linux-doc@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> To: kvmarm@lists.cs.columbia.edu
> ---
> Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
>
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
>
> --
> 2.7.5
>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
2020-08-12 14:05 ` Pingfan Liu
(?)
@ 2020-08-26 18:09 ` James Morse
-1 siblings, 0 replies; 12+ messages in thread
From: James Morse @ 2020-08-26 18:09 UTC (permalink / raw)
To: Pingfan Liu
Cc: kvmarm, Russell King, Marc Zyngier, Julien Thierry,
Suzuki K Poulose, linux-doc, linux-arm-kernel
Hi Pingfan,
On 12/08/2020 15:05, Pingfan Liu wrote:
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
We want to remove some extra work kexec does on arm64, and both implementations of
HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
I don't think we should remove this. KVM on 32bit was the only implementer, but if there
ever is another, this is how it should work.
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
(I don't think disable the D-cache is what the bit does, it forces the attributes that are
used for a data access).
Please just describe this as the on arm64 the D and I bits are cleared.
(it might be true on 32bit, I can't work the assembly out).
Thanks,
James
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-26 18:09 ` James Morse
0 siblings, 0 replies; 12+ messages in thread
From: James Morse @ 2020-08-26 18:09 UTC (permalink / raw)
To: Pingfan Liu
Cc: Marc Zyngier, linux-doc, Russell King, linux-arm-kernel, kvmarm
Hi Pingfan,
On 12/08/2020 15:05, Pingfan Liu wrote:
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
We want to remove some extra work kexec does on arm64, and both implementations of
HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
I don't think we should remove this. KVM on 32bit was the only implementer, but if there
ever is another, this is how it should work.
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
(I don't think disable the D-cache is what the bit does, it forces the attributes that are
used for a data access).
Please just describe this as the on arm64 the D and I bits are cleared.
(it might be true on 32bit, I can't work the assembly out).
Thanks,
James
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-26 18:09 ` James Morse
0 siblings, 0 replies; 12+ messages in thread
From: James Morse @ 2020-08-26 18:09 UTC (permalink / raw)
To: Pingfan Liu
Cc: Suzuki K Poulose, Marc Zyngier, linux-doc, Russell King,
linux-arm-kernel, kvmarm, Julien Thierry
Hi Pingfan,
On 12/08/2020 15:05, Pingfan Liu wrote:
> Both arm and arm64 kernel entry point have the following prerequisite:
> MMU = off, D-cache = off, I-cache = dont care.
>
> HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> new kernel.
I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
We want to remove some extra work kexec does on arm64, and both implementations of
HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
> Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> off, and KVM resets them when its unload. These are achieved by
> HVC_RESET_VECTORS call.
>
> Improve the document.
> diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> index d9eba93..a95bc30 100644
> --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
>
> * ::
>
> - r0/x0 = HVC_RESET_VECTORS
> + x0 = HVC_RESET_VECTORS (arm64 only)
>
> - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> stubs' exception vector value. This effectively disables an existing
> hypervisor.
I don't think we should remove this. KVM on 32bit was the only implementer, but if there
ever is another, this is how it should work.
> @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> x3 = x1's value when entering the next payload (arm64)
> x4 = x2's value when entering the next payload (arm64)
>
> - Mask all exceptions, disable the MMU, move the arguments into place
> + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> (arm64 only), and jump to the restart address while at HYP/EL2. This
> hypercall is not expected to return to its caller.
(I don't think disable the D-cache is what the bit does, it forces the attributes that are
used for a data access).
Please just describe this as the on arm64 the D and I bits are cleared.
(it might be true on 32bit, I can't work the assembly out).
Thanks,
James
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
2020-08-26 18:09 ` James Morse
(?)
@ 2020-08-28 8:41 ` Pingfan Liu
-1 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-28 8:41 UTC (permalink / raw)
To: James Morse
Cc: kvmarm, Russell King, Marc Zyngier, Julien Thierry,
Suzuki K Poulose, linux-doc, linux-arm-kernel
On Thu, Aug 27, 2020 at 2:10 AM James Morse <james.morse@arm.com> wrote:
>
> Hi Pingfan,
>
> On 12/08/2020 15:05, Pingfan Liu wrote:
> > Both arm and arm64 kernel entry point have the following prerequisite:
> > MMU = off, D-cache = off, I-cache = dont care.
> >
> > HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> > new kernel.
>
> I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
Yes, it is a wrong way.
>
> We want to remove some extra work kexec does on arm64, and both implementations of
> HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
> that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
>
>
> > Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> > off, and KVM resets them when its unload. These are achieved by
> > HVC_RESET_VECTORS call.
> >
> > Improve the document.
>
>
> > diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> > index d9eba93..a95bc30 100644
> > --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> > +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> > @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> >
> > * ::
> >
> > - r0/x0 = HVC_RESET_VECTORS
> > + x0 = HVC_RESET_VECTORS (arm64 only)
> >
> > - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> > + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> > stubs' exception vector value. This effectively disables an existing
> > hypervisor.
>
> I don't think we should remove this. KVM on 32bit was the only implementer, but if there
> ever is another, this is how it should work.
>
>
> > @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> > x3 = x1's value when entering the next payload (arm64)
> > x4 = x2's value when entering the next payload (arm64)
> >
> > - Mask all exceptions, disable the MMU, move the arguments into place
> > + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> > (arm64 only), and jump to the restart address while at HYP/EL2. This
> > hypercall is not expected to return to its caller.
>
> (I don't think disable the D-cache is what the bit does, it forces the attributes that are
> used for a data access).
>
> Please just describe this as the on arm64 the D and I bits are cleared.
OK, I will do it.
> (it might be true on 32bit, I can't work the assembly out).
I will leave 32bit as it is.
Thanks,
Pingfan
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-28 8:41 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-28 8:41 UTC (permalink / raw)
To: James Morse
Cc: Marc Zyngier, linux-doc, Russell King, linux-arm-kernel, kvmarm
On Thu, Aug 27, 2020 at 2:10 AM James Morse <james.morse@arm.com> wrote:
>
> Hi Pingfan,
>
> On 12/08/2020 15:05, Pingfan Liu wrote:
> > Both arm and arm64 kernel entry point have the following prerequisite:
> > MMU = off, D-cache = off, I-cache = dont care.
> >
> > HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> > new kernel.
>
> I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
Yes, it is a wrong way.
>
> We want to remove some extra work kexec does on arm64, and both implementations of
> HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
> that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
>
>
> > Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> > off, and KVM resets them when its unload. These are achieved by
> > HVC_RESET_VECTORS call.
> >
> > Improve the document.
>
>
> > diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> > index d9eba93..a95bc30 100644
> > --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> > +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> > @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> >
> > * ::
> >
> > - r0/x0 = HVC_RESET_VECTORS
> > + x0 = HVC_RESET_VECTORS (arm64 only)
> >
> > - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> > + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> > stubs' exception vector value. This effectively disables an existing
> > hypervisor.
>
> I don't think we should remove this. KVM on 32bit was the only implementer, but if there
> ever is another, this is how it should work.
>
>
> > @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> > x3 = x1's value when entering the next payload (arm64)
> > x4 = x2's value when entering the next payload (arm64)
> >
> > - Mask all exceptions, disable the MMU, move the arguments into place
> > + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> > (arm64 only), and jump to the restart address while at HYP/EL2. This
> > hypercall is not expected to return to its caller.
>
> (I don't think disable the D-cache is what the bit does, it forces the attributes that are
> used for a data access).
>
> Please just describe this as the on arm64 the D and I bits are cleared.
OK, I will do it.
> (it might be true on 32bit, I can't work the assembly out).
I will leave 32bit as it is.
Thanks,
Pingfan
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
@ 2020-08-28 8:41 ` Pingfan Liu
0 siblings, 0 replies; 12+ messages in thread
From: Pingfan Liu @ 2020-08-28 8:41 UTC (permalink / raw)
To: James Morse
Cc: Suzuki K Poulose, Marc Zyngier, linux-doc, Russell King,
linux-arm-kernel, kvmarm, Julien Thierry
On Thu, Aug 27, 2020 at 2:10 AM James Morse <james.morse@arm.com> wrote:
>
> Hi Pingfan,
>
> On 12/08/2020 15:05, Pingfan Liu wrote:
> > Both arm and arm64 kernel entry point have the following prerequisite:
> > MMU = off, D-cache = off, I-cache = dont care.
> >
> > HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
> > new kernel.
>
> I think you have this the wrong way up. This should describe what HVC_SOFT_RESTART does.
Yes, it is a wrong way.
>
> We want to remove some extra work kexec does on arm64, and both implementations of
> HVC_SOFT_RESTART on arm64 already do what we need. The change here should be to document
> that the D/I bits are cleared after a HVC_SOFT_RESTART on arm64.
>
>
> > Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
> > off, and KVM resets them when its unload. These are achieved by
> > HVC_RESET_VECTORS call.
> >
> > Improve the document.
>
>
> > diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
> > index d9eba93..a95bc30 100644
> > --- a/Documentation/virt/kvm/arm/hyp-abi.rst
> > +++ b/Documentation/virt/kvm/arm/hyp-abi.rst
> > @@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> >
> > * ::
> >
> > - r0/x0 = HVC_RESET_VECTORS
> > + x0 = HVC_RESET_VECTORS (arm64 only)
> >
> > - Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
> > + Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
> > stubs' exception vector value. This effectively disables an existing
> > hypervisor.
>
> I don't think we should remove this. KVM on 32bit was the only implementer, but if there
> ever is another, this is how it should work.
>
>
> > @@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
> > x3 = x1's value when entering the next payload (arm64)
> > x4 = x2's value when entering the next payload (arm64)
> >
> > - Mask all exceptions, disable the MMU, move the arguments into place
> > + Mask all exceptions, disable the MMU and D-cache, move the arguments into place
> > (arm64 only), and jump to the restart address while at HYP/EL2. This
> > hypercall is not expected to return to its caller.
>
> (I don't think disable the D-cache is what the bit does, it forces the attributes that are
> used for a data access).
>
> Please just describe this as the on arm64 the D and I bits are cleared.
OK, I will do it.
> (it might be true on 32bit, I can't work the assembly out).
I will leave 32bit as it is.
Thanks,
Pingfan
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2020-08-28 11:23 UTC | newest]
Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-12 14:05 [PATCH] arm(64)/kvm: improve the documentation about HVC calls Pingfan Liu
2020-08-12 14:05 ` Pingfan Liu
2020-08-12 14:05 ` Pingfan Liu
2020-08-12 14:14 ` Pingfan Liu
2020-08-12 14:14 ` Pingfan Liu
2020-08-12 14:14 ` Pingfan Liu
2020-08-26 18:09 ` James Morse
2020-08-26 18:09 ` James Morse
2020-08-26 18:09 ` James Morse
2020-08-28 8:41 ` Pingfan Liu
2020-08-28 8:41 ` Pingfan Liu
2020-08-28 8:41 ` Pingfan Liu
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