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Date: Thu, 2 Jan 2020 14:21:06 -0800
From: Ram Pai <linuxram@us.ibm.com>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
References: <20191216041924.42318-1-aik@ozlabs.ru>
 <20191216041924.42318-5-aik@ozlabs.ru>
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Subject: Re: [PATCH kernel v2 4/4] powerpc/pseries/svm: Allow IOMMU to work in
 SVM
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Reply-To: Ram Pai <linuxram@us.ibm.com>
Cc: Michael Anderson <andmike@linux.ibm.com>, kvm-ppc@vger.kernel.org,
 linuxppc-dev@lists.ozlabs.org, Thiago Jung Bauermann <bauerman@linux.ibm.com>,
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Mon, Dec 16, 2019 at 03:19:24PM +1100, Alexey Kardashevskiy wrote:
> H_PUT_TCE_INDIRECT uses a shared page to send up to 512 TCE to
> a hypervisor in a single hypercall.

Actually H_PUT_TCE_INDIRECT never used shared page.  It would have
used shared pages if the 'shared-page' solution was accepted. :)



> This does not work for secure VMs
> as the page needs to be shared or the VM should use H_PUT_TCE instead.

Maybe you should say something like this.. ?

H_PUT_TCE_INDIRECT does not work for secure VMs, since the page
containing the TCE entries is not accessible to the hypervisor.

> 
> This disables H_PUT_TCE_INDIRECT by clearing the FW_FEATURE_PUT_TCE_IND
> feature bit so SVMs will map TCEs using H_PUT_TCE.
> 
> This is not a part of init_svm() as it is called too late after FW
> patching is done and may result in a warning like this:
> 
> [    3.727716] Firmware features changed after feature patching!
> [    3.727965] WARNING: CPU: 0 PID: 1 at (...)arch/powerpc/lib/feature-fixups.c:466 check_features+0xa4/0xc0
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>


Reviewed-by: Ram Pai <linuxram@us.ibm.com>


> ---
> Changes:
> v2
> * new in the patchset
> ---
>  arch/powerpc/platforms/pseries/firmware.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/firmware.c b/arch/powerpc/platforms/pseries/firmware.c
> index d3acff23f2e3..3e49cc23a97a 100644
> --- a/arch/powerpc/platforms/pseries/firmware.c
> +++ b/arch/powerpc/platforms/pseries/firmware.c
> @@ -22,6 +22,7 @@
>  #include <asm/firmware.h>
>  #include <asm/prom.h>
>  #include <asm/udbg.h>
> +#include <asm/svm.h>
> 
>  #include "pseries.h"
> 
> @@ -101,6 +102,12 @@ static void __init fw_hypertas_feature_init(const char *hypertas,
>  		}
>  	}
> 
> +	if (is_secure_guest() &&
> +	    (powerpc_firmware_features & FW_FEATURE_PUT_TCE_IND)) {
> +		powerpc_firmware_features &= ~FW_FEATURE_PUT_TCE_IND;
> +		pr_debug("SVM: disabling PUT_TCE_IND firmware feature\n");
> +	}
> +
>  	pr_debug(" <- fw_hypertas_feature_init()\n");
>  }
> 
> -- 
> 2.17.1

-- 
Ram Pai