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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US On 15.01.21 04:11, Stefano Stabellini wrote: Hi Stefano > On Tue, 12 Jan 2021, Oleksandr Tyshchenko wrote: >> From: Oleksandr Tyshchenko >> >> We need to send mapcache invalidation request to qemu/demu everytime >> the page gets removed from a guest. >> >> At the moment, the Arm code doesn't explicitely remove the existing >> mapping before inserting the new mapping. Instead, this is done >> implicitely by __p2m_set_entry(). >> >> So we need to recognize a case when old entry is a RAM page *and* >> the new MFN is different in order to set the corresponding flag. >> The most suitable place to do this is p2m_free_entry(), there >> we can find the correct leaf type. The invalidation request >> will be sent in do_trap_hypercall() later on. >> >> Taking into the account the following the do_trap_hypercall() >> is the best place to send invalidation request: >> - The only way a guest can modify its P2M on Arm is via an hypercall >> - When sending the invalidation request, the vCPU will be blocked >> until all the IOREQ servers have acknowledged the invalidation >> >> Signed-off-by: Oleksandr Tyshchenko >> CC: Julien Grall >> [On Arm only] >> Tested-by: Wei Chen >> >> --- >> Please note, this is a split/cleanup/hardening of Julien's PoC: >> "Add support for Guest IO forwarding to a device emulator" >> >> *** >> Please note, this patch depends on the following which is >> on review: >> https://patchwork.kernel.org/patch/11803383/ >> >> This patch is on par with x86 code (whether it is buggy or not). >> If there is a need to improve/harden something, this can be done on >> a follow-up. >> *** >> >> Changes V1 -> V2: >> - new patch, some changes were derived from (+ new explanation): >> xen/ioreq: Make x86's invalidate qemu mapcache handling common >> - put setting of the flag into __p2m_set_entry() >> - clarify the conditions when the flag should be set >> - use domain_has_ioreq_server() >> - update do_trap_hypercall() by adding local variable >> >> Changes V2 -> V3: >> - update patch description >> - move check to p2m_free_entry() >> - add a comment >> - use "curr" instead of "v" in do_trap_hypercall() >> >> Changes V3 -> V4: >> - update patch description >> - re-order check in p2m_free_entry() to call domain_has_ioreq_server() >> only if p2m->domain == current->domain >> - add a comment in do_trap_hypercall() >> --- >> xen/arch/arm/p2m.c | 25 +++++++++++++++++-------- >> xen/arch/arm/traps.c | 20 +++++++++++++++++--- >> 2 files changed, 34 insertions(+), 11 deletions(-) >> >> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c >> index d41c4fa..26acb95d 100644 >> --- a/xen/arch/arm/p2m.c >> +++ b/xen/arch/arm/p2m.c >> @@ -1,6 +1,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -749,17 +750,25 @@ static void p2m_free_entry(struct p2m_domain *p2m, >> if ( !p2m_is_valid(entry) ) >> return; >> >> - /* Nothing to do but updating the stats if the entry is a super-page. */ >> - if ( p2m_is_superpage(entry, level) ) >> + if ( p2m_is_superpage(entry, level) || (level == 3) ) >> { >> - p2m->stats.mappings[level]--; >> - return; >> - } >> +#ifdef CONFIG_IOREQ_SERVER >> + /* >> + * If this gets called (non-recursively) then either the entry >> + * was replaced by an entry with a different base (valid case) or >> + * the shattering of a superpage was failed (error case). >> + * So, at worst, the spurious mapcache invalidation might be sent. >> + */ >> + if ( (p2m->domain == current->domain) && >> + domain_has_ioreq_server(p2m->domain) && >> + p2m_is_ram(entry.p2m.type) ) >> + p2m->domain->mapcache_invalidate = true; >> +#endif >> >> - if ( level == 3 ) >> - { >> p2m->stats.mappings[level]--; >> - p2m_put_l3_page(entry); >> + /* Nothing to do if the entry is a super-page. */ >> + if ( level == 3 ) >> + p2m_put_l3_page(entry); >> return; >> } >> >> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c >> index 35094d8..1070d1b 100644 >> --- a/xen/arch/arm/traps.c >> +++ b/xen/arch/arm/traps.c >> @@ -1443,6 +1443,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr, >> const union hsr hsr) >> { >> arm_hypercall_fn_t call = NULL; >> + struct vcpu *curr = current; >> >> BUILD_BUG_ON(NR_hypercalls < ARRAY_SIZE(arm_hypercall_table) ); >> >> @@ -1459,7 +1460,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr, >> return; >> } >> >> - current->hcall_preempted = false; >> + curr->hcall_preempted = false; >> >> perfc_incra(hypercalls, *nr); >> call = arm_hypercall_table[*nr].fn; >> @@ -1472,7 +1473,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr, >> HYPERCALL_RESULT_REG(regs) = call(HYPERCALL_ARGS(regs)); >> >> #ifndef NDEBUG >> - if ( !current->hcall_preempted ) >> + if ( !curr->hcall_preempted ) >> { >> /* Deliberately corrupt parameter regs used by this hypercall. */ >> switch ( arm_hypercall_table[*nr].nr_args ) { >> @@ -1489,8 +1490,21 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr, >> #endif >> >> /* Ensure the hypercall trap instruction is re-executed. */ >> - if ( current->hcall_preempted ) >> + if ( curr->hcall_preempted ) >> regs->pc -= 4; /* re-execute 'hvc #XEN_HYPERCALL_TAG' */ >> + >> +#ifdef CONFIG_IOREQ_SERVER >> + /* >> + * Taking into the account the following the do_trap_hypercall() >> + * is the best place to send invalidation request: >> + * - The only way a guest can modify its P2M on Arm is via an hypercall >> + * - When sending the invalidation request, the vCPU will be blocked >> + * until all the IOREQ servers have acknowledged the invalidation > NIT: I suggest to reword it as follows to make it sound better. > > We call ioreq_signal_mapcache_invalidate from do_trap_hypercall() > because the only way a guest can modify its P2M on Arm is via an > hypercall. Note that sending the invalidation request causes the vCPU to > block until all the IOREQ servers have acknowledged the invalidation. Agree > > > Could be done on commit. Thank you, I am preparing V5, so will update. > > Reviewed-by: Stefano Stabellini Thanks. > > >> + */ >> + if ( unlikely(curr->domain->mapcache_invalidate) && >> + test_and_clear_bool(curr->domain->mapcache_invalidate) ) >> + ioreq_signal_mapcache_invalidate(); >> +#endif >> } >> >> void arch_hypercall_tasklet_result(struct vcpu *v, long res) >> -- >> 2.7.4 >> -- Regards, Oleksandr Tyshchenko