Re: [PATCH 6/6] drivers/virt: pkvm: Intercept ioremap using pKVM MMIO_GUARD hypercall

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Will Deacon <will@kernel.org> writes:

> Hook up pKVM's MMIO_GUARD hypercall so that ioremap() and friends will
> register the target physical address as MMIO with the hypervisor,
> allowing guest exits to that page to be emulated by the host with full
> syndrome information.
>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  Documentation/virt/kvm/arm/hypercalls.rst     | 26 ++++++++++++++
>  drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c | 35 +++++++++++++++++++
>  include/linux/arm-smccc.h                     |  7 ++++
>  3 files changed, 68 insertions(+)
>
> diff --git a/Documentation/virt/kvm/arm/hypercalls.rst b/Documentation/virt/kvm/arm/hypercalls.rst
> index c42580e71bf8..af7bc2c2e0cb 100644
> --- a/Documentation/virt/kvm/arm/hypercalls.rst
> +++ b/Documentation/virt/kvm/arm/hypercalls.rst
> @@ -116,3 +116,29 @@ memory protection granule advertised by ``ARM_SMCCC_KVM_FUNC_HYP_MEMINFO``.
>  |                     |          |    +---------------------------------------------+
>  |                     |          |    | ``INVALID_PARAMETER (-3)``                  |
>  +---------------------+----------+----+---------------------------------------------+
> +
> +``ARM_SMCCC_KVM_FUNC_MMIO_GUARD``
> +----------------------------------
> +
> +Request that a given memory region is handled as MMIO by the hypervisor,
> +allowing accesses to this region to be emulated by the KVM host. The size of the
> +region is equal to the memory protection granule advertised by
> +``ARM_SMCCC_KVM_FUNC_HYP_MEMINFO``.
> +
> ++---------------------+-------------------------------------------------------------+
> +| Presence:           | Optional; pKVM protected guests only.                       |
> ++---------------------+-------------------------------------------------------------+
> +| Calling convention: | HVC64                                                       |
> ++---------------------+----------+--------------------------------------------------+
> +| Function ID:        | (uint32) | 0xC6000007                                       |
> ++---------------------+----------+----+---------------------------------------------+
> +| Arguments:          | (uint64) | R1 | Base IPA of MMIO memory region              |
> +|                     +----------+----+---------------------------------------------+
> +|                     | (uint64) | R2 | Reserved / Must be zero                     |
> +|                     +----------+----+---------------------------------------------+
> +|                     | (uint64) | R3 | Reserved / Must be zero                     |
> ++---------------------+----------+----+---------------------------------------------+
> +| Return Values:      | (int64)  | R0 | ``SUCCESS (0)``                             |
> +|                     |          |    +---------------------------------------------+
> +|                     |          |    | ``INVALID_PARAMETER (-3)``                  |
> ++---------------------+----------+----+---------------------------------------------+
>

Ok you need a SMCCC call not just a pgprot_t update. 

> diff --git a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
> index 8256cf68fd76..56a3859dda8a 100644
> --- a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
> +++ b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
> @@ -9,8 +9,10 @@
>  
>  #include <linux/arm-smccc.h>
>  #include <linux/array_size.h>
> +#include <linux/io.h>
>  #include <linux/mem_encrypt.h>
>  #include <linux/mm.h>
> +#include <linux/pgtable.h>
>  
>  #include <asm/hypervisor.h>
>  
> @@ -67,6 +69,36 @@ static const struct arm64_mem_crypt_ops pkvm_crypt_ops = {
>  	.decrypt	= pkvm_set_memory_decrypted,
>  };
>  
> +static int mmio_guard_ioremap_hook(phys_addr_t phys, size_t size,
> +				   pgprot_t *prot)
> +{
> +	phys_addr_t end;
> +	pteval_t protval = pgprot_val(*prot);
> +
> +	/*
> +	 * We only expect MMIO emulation for regions mapped with device
> +	 * attributes.
> +	 */
> +	if (protval != PROT_DEVICE_nGnRE && protval != PROT_DEVICE_nGnRnE)
> +		return 0;
> +
> +	phys = PAGE_ALIGN_DOWN(phys);
> +	end = phys + PAGE_ALIGN(size);
> +
> +	while (phys < end) {
> +		const int func_id = ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_FUNC_ID;
> +		int err;
> +
> +		err = arm_smccc_do_one_page(func_id, phys);
> +		if (err)
> +			return err;
> +
> +		phys += PAGE_SIZE;
> +	}
> +
> +	return 0;
> +}
> +
>  void pkvm_init_hyp_services(void)
>  {
>  	int i;
> @@ -89,4 +121,7 @@ void pkvm_init_hyp_services(void)
>  
>  	pkvm_granule = res.a0;
>  	arm64_mem_crypt_ops_register(&pkvm_crypt_ops);
> +
> +	if (kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_MMIO_GUARD))
> +		arm64_ioremap_prot_hook_register(&mmio_guard_ioremap_hook);
>  }
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index 9cb7c95920b0..e93c1f7cea70 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -118,6 +118,7 @@
>  #define ARM_SMCCC_KVM_FUNC_HYP_MEMINFO		2
>  #define ARM_SMCCC_KVM_FUNC_MEM_SHARE		3
>  #define ARM_SMCCC_KVM_FUNC_MEM_UNSHARE		4
> +#define ARM_SMCCC_KVM_FUNC_MMIO_GUARD		7
>  #define ARM_SMCCC_KVM_FUNC_FEATURES_2		127
>  #define ARM_SMCCC_KVM_NUM_FUNCS			128
>  
> @@ -158,6 +159,12 @@
>  			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
>  			   ARM_SMCCC_KVM_FUNC_MEM_UNSHARE)
>  
> +#define ARM_SMCCC_VENDOR_HYP_KVM_MMIO_GUARD_FUNC_ID			\
> +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
> +			   ARM_SMCCC_SMC_64,				\
> +			   ARM_SMCCC_OWNER_VENDOR_HYP,			\
> +			   ARM_SMCCC_KVM_FUNC_MMIO_GUARD)
> +
>  /* ptp_kvm counter type ID */
>  #define KVM_PTP_VIRT_COUNTER			0
>  #define KVM_PTP_PHYS_COUNTER			1
> -- 
> 2.46.0.rc1.232.g9752f9e123-goog