Re: [PATCH] arm(64)/kvm: improve the documentation about HVC calls
From: Pingfan Liu <hidden>
Date: 2020-08-12 14:14:31
Also in:
kvmarm, linux-arm-kernel
This issue is detected by Morse (https://lore.kernel.org/linux-arm-kernel/9b0da257-785b-90ba-de3c-b9ee9ccdeeba@arm.com/ (local)) 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 [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <redacted> Cc: James Morse <james.morse@arm.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Marc Zyngier <maz@kernel.org> Cc: Julien Thierry <redacted> 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