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Re: [PATCH resend v2 1/5] tpm: mark correct memory region range dirty wh

From: David Hildenbrand
Subject: Re: [PATCH resend v2 1/5] tpm: mark correct memory region range dirty when clearing RAM
Date: Fri, 23 Jul 2021 21:15:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 23.07.21 16:52, Peter Xu wrote:
On Tue, Jul 20, 2021 at 03:03:00PM +0200, David Hildenbrand wrote:
@@ -30,11 +30,13 @@ void tpm_ppi_reset(TPMPPI *tpmppi)
          QTAILQ_FOREACH(block, &guest_phys_blocks.head, next) {
+            ram_addr_t mr_start = memory_region_get_ram_addr(block->mr);
                                   block->target_end - block->target_start);
              memset(block->host_addr, 0,
                     block->target_end - block->target_start);
-            memory_region_set_dirty(block->mr, 0,
+            memory_region_set_dirty(block->mr, block->target_start - mr_start,
                                      block->target_end - block->target_start);

target_start should falls in gpa range, while mr_start is ram_addr_t.  I am not
sure whether this is right..

When I wrote that code I was under the impression that memory_region_get_ram_addr() would give the GPA where the memory region starts, but ... that's not correct as you point out. "offset" confusion :)

Neither do I know how to get correct mr offset with the existing info we've got
from GuestPhysBlock.  Maybe we need to teach guest_phys_blocks_region_add() to
also record section->offset_within_region?

We might actually want offset_within_address_space + offset_within_region, so we can calculate the GPA difference to see where inside the ramblock we end up.

I'll have a look next week, thanks for noticing!


David / dhildenb

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