Re: [PATCH 3/4 V3] Remap the device table of IOMMU in encrypted manner for kdump

Baoquan He
2018-06-22T02:52:47Z

On 06/21/18 at 08:12am, Tom Lendacky wrote:
> On 6/21/2018 3:39 AM, Baoquan He wrote:
> > On 06/21/18 at 01:42pm, lijiang wrote:
> >> 在 2018年06月21日 00:42, Tom Lendacky 写道:
> >>> On 6/16/2018 3:27 AM, Lianbo Jiang wrote:
> >>>> In kdump mode, it will copy the device table of IOMMU from the old
> >>>> device table, which is encrypted when SME is enabled in the first
> >>>> kernel. So we must remap it in encrypted manner in order to be
> >>>> automatically decrypted when we read.
> >>>>
> >>>> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
> >>>> ---
> >>>> Some changes:
> >>>> 1. add some comments
> >>>> 2. clean compile warning.
> >>>>
> >>>> drivers/iommu/amd_iommu_init.c | 15 ++++++++++++++-
> >>>> 1 file changed, 14 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> >>>> index 904c575..a20af4c 100644
> >>>> --- a/drivers/iommu/amd_iommu_init.c
> >>>> +++ b/drivers/iommu/amd_iommu_init.c
> >>>> @@ -889,11 +889,24 @@ static bool copy_device_table(void)
> >>>> }
> >>>>
> >>>> old_devtb_phys = entry & PAGE_MASK;
> >>>> +
> >>>> + /*
> >>>> + * When sme enable in the first kernel, old_devtb_phys includes the
> >>>> + * memory encryption mask(sme_me_mask), we must remove the memory
> >>>> + * encryption mask to obtain the true physical address in kdump mode.
> >>>> + */
> >>>> + if (mem_encrypt_active() && is_kdump_kernel())
> >>>> + old_devtb_phys = __sme_clr(old_devtb_phys);
> >>>> +
> >>>
> >>> You can probably just use "if (is_kdump_kernel())" here, since memory
> >>> encryption is either on in both the first and second kernel or off in
> >>> both the first and second kernel. At which point __sme_clr() will do
> >>> the proper thing.
> >>>
> >>> Actually, this needs to be done no matter what. When doing either the
> >>> ioremap_encrypted() or the memremap(), the physical address should not
> >>> include the encryption bit/mask.
> >>>
> >>> Thanks,
> >>> Tom
> >>>
> >> Thanks for your comments. If we don't remove the memory encryption mask, it will
> >> return false because the 'old_devtb_phys >= 0x100000000ULL' may become true.
> >
> > Lianbo, you may not get what Tom suggested. Tom means no matter what it
> > is, encrypted or not in 1st kernel, we need get pure physicall address,
> > and using below code is always right for both cases.
> >
> > if (is_kdump_kernel())
> > old_devtb_phys = __sme_clr(old_devtb_phys);
> >
> > And this is simpler. You even can add one line of code comment to say
> > like "Physical address w/o encryption mask is needed here."
>
> Even simpler, there's no need to even check for is_kdump_kernel(). The
> __sme_clr() should always be done if the physical address is going to be
> used for some form of io or memory remapping.
>
> So you could just change the existing:
>
> old_devtb_phys = entry & PAGE_MASK;
>
> to:
>
> old_devtb_phys = __sme_clr(entry) & PAGE_MASK;

Agree, this is even better.

>
> >>
> >> Lianbo
> >>>> if (old_devtb_phys >= 0x100000000ULL) {
> >>>> pr_err("The address of old device table is above 4G, not trustworthy!\n");
> >>>> return false;
> >>>> }
> >>>> - old_devtb = memremap(old_devtb_phys, dev_table_size, MEMREMAP_WB);
> >>>> + old_devtb = (mem_encrypt_active() && is_kdump_kernel())
> >>>> + ? (__force void *)ioremap_encrypted(old_devtb_phys,
> >>>> + dev_table_size)
> >>>> + : memremap(old_devtb_phys, dev_table_size, MEMREMAP_WB);> +
> >>>> if (!old_devtb)
> >>>> return false;
> >>>>
> >>>>
> >>
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