linux-kernel - Re: [PATCH 1/6] KVM: SEV: use mutex guard in snp_launch

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Message-ID: <c589418d-dc2e-4229-8f3c-fb49d8f9c45a@amd.com>
Date: Tue, 30 Dec 2025 15:10:43 +0100
From: "Gupta, Pankaj" <pankaj.gupta@....com>
To: Carlos López <clopez@...e.de>, kvm@...r.kernel.org,
 seanjc@...gle.com, pbonzini@...hat.com
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] KVM: SEV: use mutex guard in snp_launch_update()


> Simplify the error paths in snp_launch_update() by using a mutex guard,
> allowing early return instead of using gotos.
>
> Signed-off-by: Carlos López <clopez@...e.de>
> ---
>   arch/x86/kvm/svm/sev.c | 32 +++++++++++++-------------------
>   1 file changed, 13 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index f59c65abe3cf..1b325ae61d15 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -8,6 +8,7 @@
>    */
>   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>   
> +#include <linux/cleanup.h>

This does not seem to be required, as compiling without this as well.

Otherwise looks fine:

Reviewed-by: Pankaj Gupta <pankaj.gupta@....com>

>   #include <linux/kvm_types.h>
>   #include <linux/kvm_host.h>
>   #include <linux/kernel.h>
> @@ -2367,7 +2368,6 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   	struct kvm_memory_slot *memslot;
>   	long npages, count;
>   	void __user *src;
> -	int ret = 0;
>   
>   	if (!sev_snp_guest(kvm) || !sev->snp_context)
>   		return -EINVAL;
> @@ -2407,13 +2407,11 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   	 * initial expected state and better guard against unexpected
>   	 * situations.
>   	 */
> -	mutex_lock(&kvm->slots_lock);
> +	guard(mutex)(&kvm->slots_lock);
>   
>   	memslot = gfn_to_memslot(kvm, params.gfn_start);
> -	if (!kvm_slot_has_gmem(memslot)) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> +	if (!kvm_slot_has_gmem(memslot))
> +		return -EINVAL;
>   
>   	sev_populate_args.sev_fd = argp->sev_fd;
>   	sev_populate_args.type = params.type;
> @@ -2425,22 +2423,18 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   		argp->error = sev_populate_args.fw_error;
>   		pr_debug("%s: kvm_gmem_populate failed, ret %ld (fw_error %d)\n",
>   			 __func__, count, argp->error);
> -		ret = -EIO;
> -	} else {
> -		params.gfn_start += count;
> -		params.len -= count * PAGE_SIZE;
> -		if (params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO)
> -			params.uaddr += count * PAGE_SIZE;
> -
> -		ret = 0;
> -		if (copy_to_user(u64_to_user_ptr(argp->data), &params, sizeof(params)))
> -			ret = -EFAULT;
> +		return -EIO;
>   	}
>   
> -out:
> -	mutex_unlock(&kvm->slots_lock);
> +	params.gfn_start += count;
> +	params.len -= count * PAGE_SIZE;
> +	if (params.type != KVM_SEV_SNP_PAGE_TYPE_ZERO)
> +		params.uaddr += count * PAGE_SIZE;
>   
> -	return ret;
> +	if (copy_to_user(u64_to_user_ptr(argp->data), &params, sizeof(params)))
> +		return -EFAULT;
> +
> +	return 0;
>   }
>   
>   static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)