From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thiago Jung Bauermann Date: Mon, 16 Dec 2019 23:19:46 +0000 Subject: Re: [PATCH kernel v2 3/4] powerpc/pseries/iommu: Separate FW_FEATURE_MULTITCE to put/stuff features Message-Id: <877e2vuact.fsf@morokweng.localdomain> List-Id: References: <20191216041924.42318-1-aik@ozlabs.ru> <20191216041924.42318-4-aik@ozlabs.ru> In-Reply-To: <20191216041924.42318-4-aik@ozlabs.ru> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Alexey Kardashevskiy Cc: Michael Anderson , Ram Pai , kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, David Gibson Alexey Kardashevskiy writes: > H_PUT_TCE_INDIRECT allows packing up to 512 TCE updates into a single > hypercall; H_STUFF_TCE can clear lots in a single hypercall too. > > However, unlike H_STUFF_TCE (which writes the same TCE to all entries), > H_PUT_TCE_INDIRECT uses a 4K page with new TCEs. In a secure VM > environment this means sharing a secure VM page with a hypervisor which > we would rather avoid. > > This splits the FW_FEATURE_MULTITCE feature into FW_FEATURE_PUT_TCE_IND > and FW_FEATURE_STUFF_TCE. "hcall-multi-tce" in > the "/rtas/ibm,hypertas-functions" device tree property sets both; > the "multitce=off" kernel command line parameter disables both. > > This should not cause behavioural change. > > Signed-off-by: Alexey Kardashevskiy Reviewed-by: Thiago Jung Bauermann Tested-by: Thiago Jung Bauermann -- Thiago Jung Bauermann IBM Linux Technology Center