linux-kernel - Re: [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor.

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Date:   Thu, 7 Nov 2019 16:58:55 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, benh@...nel.crashing.org,
        david@...son.dropbear.id.au, mpe@...erman.id.au, paulus@...abs.org,
        mdroth@...ux.vnet.ibm.com, hch@....de, andmike@...ibm.com,
        sukadev@...ux.vnet.ibm.com, mst@...hat.com, ram.n.pai@...il.com,
        cai@....pw, tglx@...utronix.de, bauerman@...ux.ibm.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page
 with the hypervisor.



On 07/11/2019 04:01, Ram Pai wrote:
> On Wed, Nov 06, 2019 at 12:58:50PM +1100, Alexey Kardashevskiy wrote:
>>
>>
>> On 05/11/2019 08:28, Ram Pai wrote:
>>> The hypervisor needs to access the contents of the page holding the TCE
>>> entries while setting up the TCE entries in the IOMMU's TCE table. For
>>> SecureVMs, since this page is encrypted, the hypervisor cannot access
>>> valid entries. Share the page with the hypervisor. This ensures that the
>>> hypervisor sees the valid entries.
>>>
>>> Signed-off-by: Ram Pai <linuxram@...ibm.com>
>>> ---
>>>  arch/powerpc/platforms/pseries/iommu.c | 20 +++++++++++++++++---
>>>  1 file changed, 17 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
>>> index 8d9c2b1..07f0847 100644
>>> --- a/arch/powerpc/platforms/pseries/iommu.c
>>> +++ b/arch/powerpc/platforms/pseries/iommu.c
>>> @@ -37,6 +37,7 @@
>>>  #include <asm/mmzone.h>
>>>  #include <asm/plpar_wrappers.h>
>>>  #include <asm/svm.h>
>>> +#include <asm/ultravisor.h>
>>>  
>>>  #include "pseries.h"
>>>  
>>> @@ -179,6 +180,19 @@ static int tce_build_pSeriesLP(struct iommu_table *tbl, long tcenum,
>>>  
>>>  static DEFINE_PER_CPU(__be64 *, tce_page);
>>>  
>>> +/*
>>> + * Allocate a tce page.  If secure VM, share the page with the hypervisor.
>>> + */
>>> +static __be64 *alloc_tce_page(void)
>>> +{
>>> +	__be64 *tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
>>> +
>>> +	if (tcep && is_secure_guest())
>>> +		uv_share_page(PHYS_PFN(__pa(tcep)), 1);
>>
>>
>> There is no matching unshare in this patch.
> 
> The page is allocated and shared, and stays that way for the life of the
> kernel. It is not explicitly unshared or freed.


Ah, fair enough, I missed that, strange that we do not free it but ok. Thanks,


>  It is however
> implicitly unshared by the guest kernel, through a UV_UNSHARE_ALL_PAGES ucall
> when the guest kernel reboots. And it also gets implicitly unshared by
> the Ultravisor/Hypervisor, if the SVM abruptly terminates.
> 
>>
>>
>>> +
>>> +	return tcep;
>>> +}
>>> +
>>>  static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
>>>  				     long npages, unsigned long uaddr,
>>>  				     enum dma_data_direction direction,
>>> @@ -206,8 +220,7 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
>>>  	 * from iommu_alloc{,_sg}()
>>>  	 */
>>>  	if (!tcep) {
>>> -		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
>>> -		/* If allocation fails, fall back to the loop implementation */
>>> +		tcep = alloc_tce_page();
>>>  		if (!tcep) {
>>>  			local_irq_restore(flags);
>>>  			return tce_build_pSeriesLP(tbl, tcenum, npages, uaddr,
>>> @@ -391,6 +404,7 @@ static int tce_clearrange_multi_pSeriesLP(unsigned long start_pfn,
>>>  	return rc;
>>>  }
>>>  
>>> +
>>
>> Unrelated.
> 
> yes. will fix it.
> 
> Thanks,
> RP
> 

-- 
Alexey