Re: [PATCH v3 kvmtool 04/13] builtin-run: Rework RAM size validation

From: Andre Przywara <andre.przywara@arm.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: will@kernel.org, julien.thierry.kdev@gmail.com, maz@kernel.org,
	suzuki.poulose@arm.com, julien@xen.org,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, james.morse@arm.com
Subject: Re: [PATCH v3 kvmtool 04/13] builtin-run: Rework RAM size validation
Date: Mon, 30 May 2022 18:13:53 +0100	[thread overview]
Message-ID: <20220530181353.777d92ae@donnerap.cambridge.arm.com> (raw)
In-Reply-To: <20220525112345.121321-5-alexandru.elisei@arm.com>

On Wed, 25 May 2022 12:23:36 +0100
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

> host_ram_size() uses sysconf() to calculate the available ram, and
> sysconf() can fail. When that happens, host_ram_size() returns 0. kvmtool
> warns the user when the configured VM ram size exceeds the size of the
> host's memory, but doesn't take into account that host_ram_size() can
> return 0. If the function returns zero, skip the warning.
> 
> Since this can only happen when the user sets the memory size (via the
> -m/--mem command line argument), skip the check entirely if the user hasn't
> set it. Move the check to kvm_run_validate_cfg(), as it checks for valid
> user configuration.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>  builtin-run.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/builtin-run.c b/builtin-run.c
> index 4fc7cbed1d17..b1accbce7da3 100644
> --- a/builtin-run.c
> +++ b/builtin-run.c
> @@ -509,6 +509,8 @@ static void kvm_run_set_real_cmdline(struct kvm *kvm)
>  
>  static void kvm_run_validate_cfg(struct kvm *kvm)
>  {
> +	u64 available_ram;

Just a nit, you can pull this declaration inside the if statement below,
IIUC you will only need it there.

Otherwise looks fine:

Reviewed-by: Andre Przywara <andre.przywara@arm.com>

> +
>  	if (kvm->cfg.kernel_filename && kvm->cfg.firmware_filename)
>  		die("Only one of --kernel or --firmware can be specified");
>  
> @@ -518,6 +520,17 @@ static void kvm_run_validate_cfg(struct kvm *kvm)
>  
>  	if (kvm->cfg.firmware_filename && kvm->cfg.initrd_filename)
>  		pr_warning("Ignoring initrd file when loading a firmware image");
> +
> +	if (kvm->cfg.ram_size) {
> +		/* User specifies RAM size in megabytes. */
> +		kvm->cfg.ram_size <<= MB_SHIFT;
> +		available_ram = host_ram_size();
> +		if (available_ram && kvm->cfg.ram_size > available_ram) {
> +			pr_warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB",
> +				(unsigned long long)kvm->cfg.ram_size >> MB_SHIFT,
> +				(unsigned long long)available_ram >> MB_SHIFT);
> +		}
> +	}
>  }
>  
>  static struct kvm *kvm_cmd_run_init(int argc, const char **argv)
> @@ -596,13 +609,6 @@ static struct kvm *kvm_cmd_run_init(int argc, const char **argv)
>  
>  	if (!kvm->cfg.ram_size)
>  		kvm->cfg.ram_size = get_ram_size(kvm->cfg.nrcpus);
> -	else
> -		kvm->cfg.ram_size <<= MB_SHIFT;
> -
> -	if (kvm->cfg.ram_size > host_ram_size())
> -		pr_warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB",
> -			(unsigned long long)kvm->cfg.ram_size >> MB_SHIFT,
> -			(unsigned long long)host_ram_size() >> MB_SHIFT);
>  
>  	if (!kvm->cfg.dev)
>  		kvm->cfg.dev = DEFAULT_KVM_DEV;

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